Making field read only - OAF

I have a requirement to restrict 'Supplier Name'(in supplier entry page) from update if attribute10 is null.

I have extended CO by including the condition,

OAViewObject VendorVo = (OAViewObject)am.findViewObject("SupplierVO");

   OAViewObject VendorVo1 = (OAViewObject)am.findViewObject("SupplierVO");

   Row VenRow = (Row)VendorVo.getCurrentRow();

   Row VenRow1 = (Row)VendorVo1.getCurrentRow();

   if(VenRow1 !=null){

      entityId = (String)VenRow1.getAttribute("Attribute10");

     paramOAPageContext.writeDiagnostics(this, "Attribute10 : entityId ", +entityId);  //26078

      if(entityId!=null){

  paramOAPageContext.writeDiagnostics(this, "Attribute10 : entityId ", +entityId);

         throw new OAException("entityId: "+entityId , OAException.ERROR);

         ((OAMessageTextInputBean)webBean.findIndexedChildRecursive("VendorName")).setReadOnly(true);

       }

    }

This restricts the supplier name from update , but at the same time, it does not let me save any change incase attribute10 is not null.