If form is of type enctype="multipart/form-data" and we are handling it's submission through Groovy Event then in the parameters Map Ofbiz does not set the multipart input parameters from request parameters.
The same are available when multipart form submission is handled through service.
The reason being the code that sets the multipart parameters in request attribute is only available in ServiceEventHandler.java and in GroovyEventHandler the multipart are never set.
So I have created a method getMultiPartParameterMap in the class UtilHttp.java and put the common logic in that method so that when getCombinedMap method is called from the GroovEventHandler the method also call getMultiPartParameterMap and in the ServiceEventHandler I have written a call for getMultiPartParameterMap method.
I am attaching the Patch Kindly Verify the same.