mx.rpc.AbstractService throws error when setting managers property to null

Steps to reproduce:
1. create an instance of mx.rpc.AbstractService or any of its subclasses
2. set the managers property to null

Actual Results:

• a runtime error (NPE) is thrown

Expected Results:

• no error expected

There is no check in the "managers" setter to see if the mgrs parameter is null. A simple null check would fix this small issue.

This issue is present in SDK 3.4 and 4.0.