Fix build demo app

AppCenterDemoApp/Assets/Plugins/Android/mainTemplate.gradle

@@ -0,0 +1,90 @@
+// This file was added to implicitly specify the gradle version.
+ // Unity fails to build the project using the default gradle version,
+ // as it's unable to recognize the attribute "<queries>" in AndroidManifest added to support Android 11.
+ // Read more here: https://developers.google.com/ar/develop/unity/android-11-build
+ // Impacting commit: https://github.com/microsoft/appcenter-sdk-android/commit/67855dd9255e74fa75e5751226870a7466343619
+
+ buildscript {
+     repositories {**ARTIFACTORYREPOSITORY**
+         mavenCentral()
+         google()
+         jcenter()
+     }
+
+     dependencies {
+         classpath 'com.android.tools.build:gradle:3.4.3'
+ **BUILD_SCRIPT_DEPS**}
+ }
+
+ allprojects {
+     repositories {**ARTIFACTORYREPOSITORY**
+         mavenCentral()
+         google()
+         jcenter()
+         flatDir {
+             dirs 'libs'
+         }
+     }
+ }
+
+ apply plugin: 'com.android.application'
+ **APPLY_PLUGINS**
+
+ dependencies {
+     implementation fileTree(dir: 'libs', include: ['*.jar'])
+ **DEPS**}
+
+ android {
+     compileSdkVersion **APIVERSION**
+     buildToolsVersion '**BUILDTOOLS**'
+
+     compileOptions {
+         sourceCompatibility JavaVersion.VERSION_1_8
+         targetCompatibility JavaVersion.VERSION_1_8
+     }
+
+     defaultConfig {
+         minSdkVersion **MINSDKVERSION**
+         targetSdkVersion **TARGETSDKVERSION**
+         applicationId '**APPLICATIONID**'
+         ndk {
+             abiFilters **ABIFILTERS**
+         }
+         versionCode **VERSIONCODE**
+         versionName '**VERSIONNAME**'
+     }
+
+     lintOptions {
+         abortOnError false
+     }
+
+     aaptOptions {
+         noCompress = ['.unity3d', '.ress', '.resource', '.obb'**STREAMING_ASSETS**]
+     }**SIGN**
+
+     buildTypes {
+         debug {
+             minifyEnabled **MINIFY_DEBUG**
+             useProguard **PROGUARD_DEBUG**
+             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-unity.txt'**USER_PROGUARD**
+             jniDebuggable true
+         }
+         release {
+             minifyEnabled **MINIFY_RELEASE**
+             useProguard **PROGUARD_RELEASE**
+             proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-unity.txt'**USER_PROGUARD****SIGNCONFIG**
+         }
+     }**PACKAGING_OPTIONS****SPLITS**
+ **BUILT_APK_LOCATION**
+     bundle {
+         language {
+             enableSplit = false
+         }
+         density {
+             enableSplit = false
+         }
+         abi {
+             enableSplit = true
+         }
+     }
+ }**SPLITS_VERSION_CODE****REPOSITORIES****SOURCE_BUILD_SETUP**

AppCenterDemoApp/Assets/Plugins/Android/mainTemplate.gradle.meta

@@ -0,0 +1,7 @@
+fileFormatVersion: 2
+guid: 5ab4bdd786d334587ac7d837c2649411
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Assets/AppCenter/Plugins/AppCenterSDK/Distribute/Android/DistributeDelegate.cs

@@ -30,7 +30,11 @@ namespace Microsoft.AppCenter.Unity.Distribute.Internal
 
         void onNoReleaseAvailable(AndroidJavaObject activity)
         {
-            Distribute.NoReleaseAvailable?.Invoke();
+            if (Distribute.NoReleaseAvailable == null)
+            {
+                return;
+            }
+            Distribute.NoReleaseAvailable.Invoke();
         }
     }
 }