Merge pull request #821 from quicktype/fix-all-properties-optional

Fix making all properties optional. Fixes #820

src/TypeBuilder.ts

@@ -330,6 +330,7 @@ export class TypeBuilder {
         properties: OrderedMap<string, ClassProperty>,
         forwardingRef?: TypeRef
     ): TypeRef {
+        properties = this.modifyPropertiesIfNecessary(properties);
         return this.getOrAddType(
             classTypeIdentity(properties),
             tr => new ClassType(tr, false, properties),