changed PLIBuilder Fixture to better maintainable code, similar to the algorithmFixture
changed ImmutableList to ArrayList, added null values
fixed PLIBuilder for null semantic
added test for nullNotEqualsNull
fixed fixture
added exception for currently not handled distinct sorted values
filter null values for sorteddistinctcolumns
updated test for null behaviour
Merge pull request #265 from Jens-Ehrlich/nullNotEqualsNull

extended PLIBuilder for null==null or null!=null semantik