fix IndexOutOfBoundsException in getType()

[Egor18]

Hi! I found out that IndexOutOfBoundsException is occurred in cases when getType() is called on parameter of a catch with multiple exception types, some of which is unknown (noclasspath mode):

java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
	at java.util.ArrayList.rangeCheck(ArrayList.java:657)
	at java.util.ArrayList.get(ArrayList.java:433)
	at spoon.support.reflect.code.CtCatchVariableImpl.getType(CtCatchVariableImpl.java:109)
        ....

I think it would be better to return null from getType() in such cases instead, so I provided this PR.

[pvojtechovsky]

could you please add assert, which checks the returned value too?
assertNull(...)

[pvojtechovsky]

Hi!
It looks good to me. I agree that null is the best returned value for that case.
Optionally we might return Exception.class, but it doesn't warn the client that value is unknown ... So I like null

[pvojtechovsky]

It would be nice to have it documented in javaDoc of CtCatchVariable#getType() too.

[pvojtechovsky]

Thank You!