code: public static void handleSetPropertyExpression(
          Object bean,
          String prop,
          String expression,
          PageContext pageContext,
          ProtectedFunctionMapper functionMapper)
          throws JspCoreException {
          try {
              Method method = getWriteMethod(bean.getClass(), prop);
              method.invoke(
                  bean,
                  new Object[] {
                       PageContextImpl.proprietaryEvaluate(
                          expression,
                          method.getParameterTypes()[0],
                          pageContext,
                          functionMapper,
                          false)});
          }
          catch (Exception ex) {
              throw new JspCoreException(ex);
          }
      }
docs: Use proprietaryEvaluate
  public static void handleSetPropertyExpression(Object bean,
  String prop, String expression, PageContext pageContext,
  VariableResolver variableResolver, FunctionMapper functionMapper )
  throws JspCoreException
  {
  try {
  Method method = getWriteMethod(bean.getClass(), prop);
  method.invoke(bean, new Object[] {
  pageContext.getExpressionEvaluator().evaluate(
  expression,
  method.getParameterTypes()[0],
  variableResolver,
  functionMapper,
  null )
  });
  } catch (Exception ex) {
  throw new JspCoreException(ex);
  }
  }