GHMilestone throws NPE on null state

[rnveach]

The following method is not null safe:

github-api/src/main/java/org/kohsuke/github/GHMilestone.java

Lines 137 to 138 in 0556380

	public GHMilestoneState getState() {
	return Enum.valueOf(GHMilestoneState.class, state.toUpperCase(Locale.ENGLISH));

Whenever it is called to get the state of the milestone, and it (state field) is null, it will throw a NullPointerException.

There is no other method in this class to ascertain the value of this before calling the method. The field is private. Programmers are forced to wrap this in a try/catch in the case it is null.

It would ease handling this call if it had a null check and returned null if there is no state.