Product Version: NetBeans IDE Dev (Build 201406040001)
Java: 1.7.0_65; Java HotSpot(TM) 64-Bit Server VM 24.65-b04
Runtime: Java(TM) SE Runtime Environment 1.7.0_65-b13
Glassfish 4 as target server

Steps to reproduce:
Create Web Project and add websocket endpoint class
Invoke add onOpen method command on this class. 
The IDE produces:
>>     @OnOpen public void onOpen(Throwable t) {}
deploying this code produces Exceptions on server:
>> javax.websocket.DeploymentException: Method:  onOpen::class java.lang.Throwable  is not allowed as parameter type for method annotated with @OnOpen.

expected function signature as described in javadoc:

The method may only take the following parameters:-
optional Session parameter
optional EndpointConfig parameter
Zero to n String parameters annotated with the PathParam annotation.

for onClose function generated code also wrong. expected:
optional Session parameter
optional CloseReason parameter
Zero to n String parameters annotated with the PathParam annotation.