java - UmbrellaException when accessing variable type List<File> (lib-gwt-file & GWT) -

i error in browser log:

uncaught com.google.gwt.event.shared.umbrellaexception: exception caught: (typeerror) : cannot read property 'add_75_g$' of undefined     castfireeventfromsource_0_g$ @ eventbus.java:77     fireeventfromsource_2_g$ @ simpleeventbus.java:67     fireevent_9_g$ @ droppanel.java:97     firenativeevent_1_g$ @ domevent.java:125     dispatch_87_g$ @ droppanel.java:125     handler_0_g$ @ droppanel.java:87 

this exception raises when try use list<file> way. using other variable type works makes me suspect might not fault. i'm inexperienced sure.

import org.vectomatic.file.file; import org.vectomatic.file.filelist;  protected list<file> readqueue; protected file fileholder;  private void processfiles(filelist files) {   for(file file : files)   {         gwt.log(file.getname());          fileholder = file; // no error         readqueue.add(file); // error     } } 

even accessing readqueue.size(); raises exception.

i'm using gwt-2.7.0 , lib-gwt-file 0.3.6.
according http://www.vectomatic.org/libs/lib-gwt-file these correct versions work together.

code compiles without errors.

i'm stuck, ideas?

never mind.. didn't use:

protected list<file> readqueue = new arraylist<file>(); 

for defense... example code did not use 1 either.