diff --git a/taskcluster/ci/release-source/kind.yml b/taskcluster/ci/release-source/kind.yml
index edee9c4870fe..95421614b0dd 100644
--- a/taskcluster/ci/release-source/kind.yml
+++ b/taskcluster/ci/release-source/kind.yml
@@ -39,7 +39,7 @@ job-defaults:
     # The build_attrs transform defaults to setting a `skip-unlles-schedules'
     # optimization based on the task label. The tasks here don't have corresponding
     # schedules defined in mozbuild.
-    optimization: {}
+    optimization: null
 
 jobs:
     firefox-source/opt:
diff --git a/taskcluster/taskgraph/transforms/balrog_submit.py b/taskcluster/taskgraph/transforms/balrog_submit.py
index c69c4f34fdba..34b54b64da30 100644
--- a/taskcluster/taskgraph/transforms/balrog_submit.py
+++ b/taskcluster/taskgraph/transforms/balrog_submit.py
@@ -21,10 +21,6 @@ from taskgraph.transforms.task import task_description_schema
 from voluptuous import Optional
 
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 balrog_description_schema = schema.extend({
     # unique label to describe this balrog task, defaults to balrog-{dep.label}
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover.py b/taskcluster/taskgraph/transforms/beetmover.py
index 0a041dc8b54a..ad0b5812e793 100644
--- a/taskcluster/taskgraph/transforms/beetmover.py
+++ b/taskcluster/taskgraph/transforms/beetmover.py
@@ -114,10 +114,6 @@ UPSTREAM_SOURCE_ARTIFACTS = [
     "source.tar.xz.asc",
 ]
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 transforms = TransformSequence()
 
 beetmover_description_schema = schema.extend({
diff --git a/taskcluster/taskgraph/transforms/beetmover_checksums.py b/taskcluster/taskgraph/transforms/beetmover_checksums.py
index 686fbf37dc84..49239ce061fd 100644
--- a/taskcluster/taskgraph/transforms/beetmover_checksums.py
+++ b/taskcluster/taskgraph/transforms/beetmover_checksums.py
@@ -22,10 +22,6 @@ from voluptuous import Optional, Required
 from taskgraph.util.treeherder import replace_group
 from taskgraph.transforms.task import task_description_schema
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_checksums_description_schema = schema.extend({
     Required('depname', default='build'): basestring,
     Required('attributes'): {basestring: object},
diff --git a/taskcluster/taskgraph/transforms/beetmover_emefree_checksums.py b/taskcluster/taskgraph/transforms/beetmover_emefree_checksums.py
index dd2aa2d760f4..e94a082b5d6f 100644
--- a/taskcluster/taskgraph/transforms/beetmover_emefree_checksums.py
+++ b/taskcluster/taskgraph/transforms/beetmover_emefree_checksums.py
@@ -14,10 +14,6 @@ from taskgraph.util.attributes import copy_attributes_from_dependent_job
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_checksums_description_schema = schema.extend({
     Required('depname', default='build'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_geckoview.py b/taskcluster/taskgraph/transforms/beetmover_geckoview.py
index 038958f8c43a..8bef23621874 100644
--- a/taskcluster/taskgraph/transforms/beetmover_geckoview.py
+++ b/taskcluster/taskgraph/transforms/beetmover_geckoview.py
@@ -37,8 +37,6 @@ _MOZ_UPDATE_CHANNEL_PER_BRANCH = {
     'maple': '-nightly-maple',
 }
 
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_description_schema = schema.extend({
     Required('depname', default='build'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_langpack_checksums.py b/taskcluster/taskgraph/transforms/beetmover_langpack_checksums.py
index 1a550fa23e5e..2606bf8d6f28 100644
--- a/taskcluster/taskgraph/transforms/beetmover_langpack_checksums.py
+++ b/taskcluster/taskgraph/transforms/beetmover_langpack_checksums.py
@@ -17,10 +17,6 @@ from taskgraph.util.scriptworker import (get_beetmover_bucket_scope,
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_checksums_description_schema = schema.extend({
     Required('depname', default='build'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_push_to_release.py b/taskcluster/taskgraph/transforms/beetmover_push_to_release.py
index 07e242a0ffa0..185241cdeef7 100644
--- a/taskcluster/taskgraph/transforms/beetmover_push_to_release.py
+++ b/taskcluster/taskgraph/transforms/beetmover_push_to_release.py
@@ -16,15 +16,9 @@ from taskgraph.util.scriptworker import (
     get_beetmover_bucket_scope, add_scope_prefix,
     get_worker_type_for_scope,
 )
-from taskgraph.transforms.job import job_description_schema
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-job_description_schema = {str(k): v for k, v in job_description_schema.schema.iteritems()}
-
 
 beetmover_push_to_release_description_schema = Schema({
     Required('name'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_repackage.py b/taskcluster/taskgraph/transforms/beetmover_repackage.py
index c4224e4941b3..2bfc9250e23d 100644
--- a/taskcluster/taskgraph/transforms/beetmover_repackage.py
+++ b/taskcluster/taskgraph/transforms/beetmover_repackage.py
@@ -136,10 +136,6 @@ UPSTREAM_ARTIFACT_SIGNED_MAR_PATHS = [
     'target.bz2.complete.mar',
 ]
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_description_schema = schema.extend({
     # depname is used in taskref's to identify the taskID of the unsigned things
     Required('depname', default='build'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_repackage_partner.py b/taskcluster/taskgraph/transforms/beetmover_repackage_partner.py
index 6188afa39277..aaec48dfe2d7 100644
--- a/taskcluster/taskgraph/transforms/beetmover_repackage_partner.py
+++ b/taskcluster/taskgraph/transforms/beetmover_repackage_partner.py
@@ -35,10 +35,6 @@ import logging
 logger = logging.getLogger(__name__)
 
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_description_schema = schema.extend({
     # depname is used in taskref's to identify the taskID of the unsigned things
     Required('depname', default='build'): basestring,
diff --git a/taskcluster/taskgraph/transforms/beetmover_source_checksums.py b/taskcluster/taskgraph/transforms/beetmover_source_checksums.py
index fd6a208832fc..fc0f4ca722f9 100644
--- a/taskcluster/taskgraph/transforms/beetmover_source_checksums.py
+++ b/taskcluster/taskgraph/transforms/beetmover_source_checksums.py
@@ -20,10 +20,6 @@ from taskgraph.util.scriptworker import (generate_beetmover_artifact_map,
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 beetmover_checksums_description_schema = schema.extend({
     Required('depname', default='build'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/checksums_signing.py b/taskcluster/taskgraph/transforms/checksums_signing.py
index 33a674784160..bc7f09808d9a 100644
--- a/taskcluster/taskgraph/transforms/checksums_signing.py
+++ b/taskcluster/taskgraph/transforms/checksums_signing.py
@@ -19,10 +19,6 @@ from taskgraph.util.treeherder import replace_group
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 checksums_signing_description_schema = schema.extend({
     Required('depname', default='beetmover'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/google_play_strings.py b/taskcluster/taskgraph/transforms/google_play_strings.py
index 7d6d6593c71f..1704aae4f666 100644
--- a/taskcluster/taskgraph/transforms/google_play_strings.py
+++ b/taskcluster/taskgraph/transforms/google_play_strings.py
@@ -13,10 +13,6 @@ from taskgraph.util.schema import resolve_keyed_by, Schema
 
 from voluptuous import Required
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 google_play_description_schema = Schema({
     Required('name'): basestring,
     Required('description'): task_description_schema['description'],
diff --git a/taskcluster/taskgraph/transforms/job/__init__.py b/taskcluster/taskgraph/transforms/job/__init__.py
index 56d920b2e60f..01a69741c717 100644
--- a/taskcluster/taskgraph/transforms/job/__init__.py
+++ b/taskcluster/taskgraph/transforms/job/__init__.py
@@ -33,10 +33,6 @@ from voluptuous import (
 
 logger = logging.getLogger(__name__)
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 # Schema for a build description
 job_description_schema = Schema({
     # The name of the job and the job's label.  At least one must be specified,
diff --git a/taskcluster/taskgraph/transforms/job/mozharness_test.py b/taskcluster/taskgraph/transforms/job/mozharness_test.py
index 28279a02c192..a51d80aa3152 100644
--- a/taskcluster/taskgraph/transforms/job/mozharness_test.py
+++ b/taskcluster/taskgraph/transforms/job/mozharness_test.py
@@ -39,8 +39,6 @@ def get_variant(test_platform):
     return ''
 
 
-test_description_schema = {str(k): v for k, v in test_description_schema.schema.iteritems()}
-
 mozharness_test_run_schema = Schema({
     Required('using'): 'mozharness-test',
     Required('test'): test_description_schema,
diff --git a/taskcluster/taskgraph/transforms/l10n.py b/taskcluster/taskgraph/transforms/l10n.py
index 0356eeaa5a93..dd5210939bc0 100644
--- a/taskcluster/taskgraph/transforms/l10n.py
+++ b/taskcluster/taskgraph/transforms/l10n.py
@@ -36,11 +36,6 @@ def _by_platform(arg):
     return optionally_keyed_by('build-platform', arg)
 
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-job_description_schema = {str(k): v for k, v in job_description_schema.schema.iteritems()}
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 l10n_description_schema = schema.extend({
     # Name for this job, inferred from the dependent job before validation
     Required('name'): basestring,
diff --git a/taskcluster/taskgraph/transforms/push_apk.py b/taskcluster/taskgraph/transforms/push_apk.py
index 78d22486e1a6..b5e60d49abeb 100644
--- a/taskcluster/taskgraph/transforms/push_apk.py
+++ b/taskcluster/taskgraph/transforms/push_apk.py
@@ -17,10 +17,6 @@ from taskgraph.util.taskcluster import get_artifact_prefix
 
 from voluptuous import Optional, Required
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 
 push_apk_description_schema = Schema({
     Required('dependent-tasks'): object,
diff --git a/taskcluster/taskgraph/transforms/release_beetmover_signed_addons.py b/taskcluster/taskgraph/transforms/release_beetmover_signed_addons.py
index ff29a20d37bd..5f14868dc5e6 100644
--- a/taskcluster/taskgraph/transforms/release_beetmover_signed_addons.py
+++ b/taskcluster/taskgraph/transforms/release_beetmover_signed_addons.py
@@ -24,9 +24,6 @@ import copy
 logger = logging.getLogger(__name__)
 
 
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
-
 transforms = TransformSequence()
 
 
diff --git a/taskcluster/taskgraph/transforms/release_generate_checksums_beetmover.py b/taskcluster/taskgraph/transforms/release_generate_checksums_beetmover.py
index 1efe12f9371a..f9d704210cdb 100644
--- a/taskcluster/taskgraph/transforms/release_generate_checksums_beetmover.py
+++ b/taskcluster/taskgraph/transforms/release_generate_checksums_beetmover.py
@@ -37,10 +37,6 @@ CHECKSUMS_SIGNING_ARTIFACTS = [
 ]
 
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 release_generate_checksums_beetmover_schema = schema.extend({
     # depname is used in taskref's to identify the taskID of the unsigned things
     Required('depname', default='build'): basestring,
diff --git a/taskcluster/taskgraph/transforms/release_generate_checksums_signing.py b/taskcluster/taskgraph/transforms/release_generate_checksums_signing.py
index a5200d1e6873..4a4d0d2dd34f 100644
--- a/taskcluster/taskgraph/transforms/release_generate_checksums_signing.py
+++ b/taskcluster/taskgraph/transforms/release_generate_checksums_signing.py
@@ -19,10 +19,6 @@ from taskgraph.util.taskcluster import get_artifact_path
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 release_generate_checksums_signing_schema = schema.extend({
     Required('depname', default='release-generate-checksums'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/release_sign_and_push_langpacks.py b/taskcluster/taskgraph/transforms/release_sign_and_push_langpacks.py
index 2f3b06f0bd9c..e466d97eb95e 100644
--- a/taskcluster/taskgraph/transforms/release_sign_and_push_langpacks.py
+++ b/taskcluster/taskgraph/transforms/release_sign_and_push_langpacks.py
@@ -14,8 +14,6 @@ from taskgraph.util.schema import resolve_keyed_by, optionally_keyed_by
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Any, Required
 
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 transforms = TransformSequence()
 
 langpack_sign_push_description_schema = schema.extend({
diff --git a/taskcluster/taskgraph/transforms/release_snap_push.py b/taskcluster/taskgraph/transforms/release_snap_push.py
index c2f02eaedbdb..f2f00dd3cfe4 100644
--- a/taskcluster/taskgraph/transforms/release_snap_push.py
+++ b/taskcluster/taskgraph/transforms/release_snap_push.py
@@ -13,10 +13,6 @@ from taskgraph.util.schema import optionally_keyed_by, resolve_keyed_by, Schema
 
 from voluptuous import Optional, Required
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 push_snap_description_schema = Schema({
     Required('name'): basestring,
     Required('job-from'): task_description_schema['job-from'],
diff --git a/taskcluster/taskgraph/transforms/repackage.py b/taskcluster/taskgraph/transforms/repackage.py
index f430fdb154a0..5c0f684ff8dc 100644
--- a/taskcluster/taskgraph/transforms/repackage.py
+++ b/taskcluster/taskgraph/transforms/repackage.py
@@ -22,10 +22,6 @@ from taskgraph.util.workertypes import worker_type_implementation
 from taskgraph.transforms.job import job_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-job_description_schema = {str(k): v for k, v in job_description_schema.schema.iteritems()}
-
 
 packaging_description_schema = schema.extend({
     # depname is used in taskref's to identify the taskID of the signed things
diff --git a/taskcluster/taskgraph/transforms/repackage_partner.py b/taskcluster/taskgraph/transforms/repackage_partner.py
index 2468acd90f5e..d379c7f8b7ac 100644
--- a/taskcluster/taskgraph/transforms/repackage_partner.py
+++ b/taskcluster/taskgraph/transforms/repackage_partner.py
@@ -24,10 +24,6 @@ from taskgraph.transforms.task import task_description_schema
 from taskgraph.transforms.repackage import PACKAGE_FORMATS
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 
 def _by_platform(arg):
     return optionally_keyed_by('build-platform', arg)
diff --git a/taskcluster/taskgraph/transforms/repackage_signing.py b/taskcluster/taskgraph/transforms/repackage_signing.py
index 0b8b12d430df..5cf9a5bb8b67 100644
--- a/taskcluster/taskgraph/transforms/repackage_signing.py
+++ b/taskcluster/taskgraph/transforms/repackage_signing.py
@@ -20,10 +20,6 @@ from taskgraph.util.scriptworker import (
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 repackage_signing_description_schema = schema.extend({
     Required('depname', default='repackage'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/repackage_signing_partner.py b/taskcluster/taskgraph/transforms/repackage_signing_partner.py
index 5889beb26590..b954808fd461 100644
--- a/taskcluster/taskgraph/transforms/repackage_signing_partner.py
+++ b/taskcluster/taskgraph/transforms/repackage_signing_partner.py
@@ -20,10 +20,6 @@ from taskgraph.util.taskcluster import get_artifact_path
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 transforms = TransformSequence()
 
 repackage_signing_description_schema = schema.extend({
diff --git a/taskcluster/taskgraph/transforms/signing.py b/taskcluster/taskgraph/transforms/signing.py
index 442c5d7cebdc..0c19257659cd 100644
--- a/taskcluster/taskgraph/transforms/signing.py
+++ b/taskcluster/taskgraph/transforms/signing.py
@@ -20,10 +20,6 @@ from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 transforms = TransformSequence()
 
 signing_description_schema = schema.extend({
diff --git a/taskcluster/taskgraph/transforms/source_checksums_signing.py b/taskcluster/taskgraph/transforms/source_checksums_signing.py
index 62cf935c91b4..2cc3e1ee36aa 100644
--- a/taskcluster/taskgraph/transforms/source_checksums_signing.py
+++ b/taskcluster/taskgraph/transforms/source_checksums_signing.py
@@ -18,10 +18,6 @@ from taskgraph.util.scriptworker import (
 from taskgraph.transforms.task import task_description_schema
 from voluptuous import Required, Optional
 
-# Voluptuous uses marker objects as dictionary *keys*, but they are not
-# comparable, so we cast all of the keys back to regular strings
-task_description_schema = {str(k): v for k, v in task_description_schema.schema.iteritems()}
-
 checksums_signing_description_schema = schema.extend({
     Required('depname', default='beetmover'): basestring,
     Optional('label'): basestring,
diff --git a/taskcluster/taskgraph/transforms/source_test.py b/taskcluster/taskgraph/transforms/source_test.py
index a4657191be27..fdd2cd845bbd 100644
--- a/taskcluster/taskgraph/transforms/source_test.py
+++ b/taskcluster/taskgraph/transforms/source_test.py
@@ -27,8 +27,6 @@ from voluptuous import (
     Schema,
 )
 
-job_description_schema = {str(k): v for k, v in job_description_schema.schema.iteritems()}
-
 source_test_description_schema = Schema({
     # most fields are passed directly through as job fields, and are not
     # repeated here
diff --git a/taskcluster/taskgraph/util/schema.py b/taskcluster/taskgraph/util/schema.py
index 96f33fb609e2..1bdf1b571c41 100644
--- a/taskcluster/taskgraph/util/schema.py
+++ b/taskcluster/taskgraph/util/schema.py
@@ -215,6 +215,9 @@ class Schema(voluptuous.Schema):
         schema.__class__ = Schema
         return schema
 
+    def __getitem__(self, item):
+        return self.schema[item]
+
 
 OptimizationSchema = voluptuous.Any(
     # always run this task (default)