code: public ValueReference getValueReference(ELContext context) {
          // Expected to be over-ridden by implementation
          context.notifyBeforeEvaluation(getExpressionString());
          context.notifyAfterEvaluation(getExpressionString());
          return null;
      }
docs: @param context The EL context for this evaluation
  
  @return This default implementation always returns <code>null</code>
  
  @since EL 2.2