Fix some statically detected code issues

This includes: unnecessary semicolons, suppress warnings, switch statements, final/private qualifiers, Optional wrapping, conditionals, both inline and non-inline variables, ternaries, Collection putAll() calls, StringBuilders, and throws declarations.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=244182539

java/google/registry/model/billing/BillingEvent.java

@@ -608,7 +608,6 @@ public abstract class BillingEvent extends ImmutableObject
       }
 
       @Override
-      @SuppressWarnings("unchecked")
       public Modification build() {
         Modification instance = getInstance();
         checkNotNull(instance.reason);