Working on #13486

This change should assign a value to the existing variable instead of declaring a new variable.  This commit breaks some tests and this branch is currently a WIP.

grails-plugin-controllers/src/main/groovy/org/grails/compiler/web/ControllerActionTransformer.java

@@ -846,7 +846,7 @@ protected void initializeCommandObjectParameter(final BlockStatement wrapper,
         final ArgumentListExpression initializeCommandObjectArguments = args(classX(commandObjectNode), constX(paramName));
         final MethodCallExpression initializeCommandObjectMethodCall = callThisX("initializeCommandObject", initializeCommandObjectArguments);
         applyDefaultMethodTarget(initializeCommandObjectMethodCall, commandObjectNode);
-        final Expression assignCommandObjectToParameter = declX(localVarX(paramName), initializeCommandObjectMethodCall);
+        final Expression assignCommandObjectToParameter = assignX(varX(paramName, commandObjectNode), initializeCommandObjectMethodCall);
         wrapper.addStatement(stmt(assignCommandObjectToParameter));
     }