XWPFNumbering.addAbstractNum will definitely throw an exception

[Sayi]

XWPFNumbering.addAbstractNum code is an if branch. There are two points to note:

1. When abstractNum.getAbstractNum () is not null, you must ensure that AbstractNumId has a value, so in order for users to find the correct AbstractNumId value, two getter methods are exposed, of course, the list cannot be modified.

2. When abstractNum.getAbstractNum () is null, an exception will be thrown when cascading the method of abstractNum.getAbstractNum (), so you need to set the attribute CtAbstractNum of the abstractNum.

PS: For the first point, we can also assert in the XWPFNumbering.addAbstractNum that AbstractNumId is not null, fail fast.

[Alain-Bearez]

applied by commit r1875747

this PR can be closed