Hi

You can use OOTB pzIsNotEmpty edit validate rule if you just want to check if the value is NULL.

You can take a look at the javacode in it if you want to customize.

Hope this helps

Hi, 

Can create an edit validate rule and add the below code with your conditions and 

keep this edit validate in the advanced tab of the property  (under "use validate").

boolean isValid = (theValue == "null" || theValue == null  || theValue == NULL );   //your condition as required 

      if (!isValid)
      {
                   theProperty.addMessage("blank");    // messaged to show in UI 

       }

       return isValid;