"You encountered a bug in the interpreter: java.lang.NullPointerException" On a unit test

[GetLocalPlayer]

During a unit test

Running <GroupTests:4 - testGroupBasic>..
	You encountered a bug in the interpreter: java.lang.NullPointerException
  at P:\WC3\WurstStdlib2\wurst\_handles\Group.wurst line 49
... when calling group_add(group612, varargs[unit606]) in GroupTests.wurst:11
... when calling testGroupBasic() in GroupTests.wurst:4

Was changing Group.wurst package

public function group.add(vararg unit units) returns integer
	var i = 0
	for u in units
		if GroupAddUnit(this, u)     // <-- This is line 49
			i += 1
	return i

[Frotty]

The compiletime implementation for GroupAddUnit has no return type, this is the issue here.