IssueDialog with PositionedStrings with undefined Locations

[BookWood7th]

## Description The Location class may be instantiated without an associated file. This causes fileUri to be null. Due to this Location::compareTo causes a NullPointerException, when used by a Location without an associated file ## Reproducible always ### Steps to reproduce > Describe the steps needed to reproduce the issue. 1. Create a Location without an associated fileUri (Location.UNDEFINED / any constructor values with fileUri set to null) 2. Create a second Location object 3. call compareTo on the first Location comparing it to the second Expected to sort by their Position objects. Actually throws NullPointerException. ### Additional information --- * Commit:

8e28439

[BookWood7th]

The issue actually does not concern Location but instead IssueDialog where sorting is done without checking for these NullPointerExceptions. May also be an edge case of Java documentation for Array.sort, which can't take Comparators that don't accept null values

[mattulbrich]

Well, compareTo should not fail for valid argument objects, so I'd say it is a bug in the comparison.

Probably easy to fix by making the comparison null-aware, isn't it?

[BookWood7th]

The issue is reasonably easy to fix and I believe I found a somewhat elegant solution to this. The proposed solution adds explicit nullsLast comparators that check for null values of fileUri and position fields in Location before using the respective natural order of these fields in Location#compareTo(Location)