code: public static Stack startIfNotOnTop(CombinedInterceptorAndDecoratorStackMethodHandler context) {
          Stack stack = getStack();
          if (stack.startIfNotOnTop(context)) {
              return stack;
          }
          return null;
      }
docs: Pushes the given context to the stack if the given context is not on top of the stack already.
  If this method return a non-null value, the caller is responsible for calling {@link #endInterceptorContext()}
  after the invocation finishes.
  @param context the given context
  @return true if the given context was pushed to the top of the stack, false if the given context was on top already