Merge pull request #38 from ThePumpingLemma/master

DistinctColumnsItems can properly handle null values, so use the TreeSet...
Merge pull request #1 from eugener/master

Update code base
Do not lazily overwrite user defined values
Added comment
Do not lazily overwrite user defined values
Do not lazily overwrite user defined values
Do not lazily overwrite user defined values
Merge pull request #39 from CroniD/master

Do not lazily overwrite user defined values