Merge pull request #1 from luka5/master

dont call construtor if value is null
removed old comparison code
Merge branch 'master' of github.com:mikanda/model
fixed another old code piece
Merge branch 'master' of github.com:mikanda/model
add integration test for reset(attr)
Merge pull request #2 from luka5/master

reset only a given attribute.
Merge branch 'master' into bugfix/set-equal-date