Milestones can not be unset

[Arrow768]

It is not possible to unset milestones.
To unset a PATCH with null for the milestone value needs to be sent.

However that is not possible due to two problems:

• public void setMilestone(GHMilestone milestone) throws a null pointer exception if null is passed.
  A check like that solves this problem:

public void setMilestone(GHMilestone milestone) throws IOException {
        if(milestone != null){
            editIssue("milestone",milestone.getNumber());
        } else {
            editIssue("milestone",null);
        }

    }

• This leads to the second problem. The editIssue method calls the method _with on the Requester which only adds arguments if the value of that argument is not null.

I solved this problem by having a editIssueNullable that calls withNullable instead of _with, but I am not sure if that is a good way to solve that problem.