GREL sort() throws NullPointerException when used on arrays that contain nulls

[thadguidry]

sort() does not work on arrays that contain null values.

To Reproduce

Steps to reproduce the behavior:

1. Perform a Transform on the following GREL expression

[ null, "E09000002", "E05000036",  null, "E14000540", null, "E30000234", "E38000004" ].sort()

Current Results

In Expression preview the following is shown:
Error: java.lang.NullPointerException

Expected Behavior

sort() should still work and perhaps default to nulls last as a convenience for users.
Optionally, a Boolean parameter could be added to sort() for users to override the default nulls last behavior.

Screenshots

Versions

• Operating System: Windows 10
• Browser Version: Firefox latest
• JRE or JDK Version: JDK8
• OpenRefine: openrefine-3.4-beta-514-gaa43445

Datasets

Additional context

I think instead of defaulting to the NullPointerException, instead we could still allow sorting of arrays that contain null values and place nulls first or last with a new sort() Boolean parameter for nullsLast.
https://github.com/OpenRefine/OpenRefine/blob/master/main/src/com/google/refine/expr/functions/arrays/Sort.java#L55
To do that we could use java.util.Comparator https://www.tutorialspoint.com/How-to-sort-an-array-of-objects-containing-null-elements-in-java