Minor update to the Mutator so that it doesn't try to update false values

[Luciam91]

This will stop the values from failing; may be a better solution?

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 3648311 on Luciam91:master into 98a582d on Miljar:master.

[Miljar]

Thanks for your contribution. I have written a more elaborate comment on this pull request in #39
Can you please either update your code, or let me know if I should take over?

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling e3edd22 on Luciam91:master into 98a582d on Miljar:master.

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 823e994 on Luciam91:master into 98a582d on Miljar:master.

[Miljar]

Can you also add these checks for the Native adapter?

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 7638eaa on Luciam91:master into 98a582d on Miljar:master.

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 7638eaa on Luciam91:master into 98a582d on Miljar:master.

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 7638eaa on Luciam91:master into 98a582d on Miljar:master.

[coveralls]

Coverage decreased (-0.25%) to 99.75% when pulling 7638eaa on Luciam91:master into 98a582d on Miljar:master.

[coveralls]

Coverage decreased (-0.51%) to 99.49% when pulling c61c855 on Luciam91:master into 98a582d on Miljar:master.

[Luciam91]

Added the test to the Native mapper as well; however I cannot for the life of me work out why the code coverage doesn't catch the exception line of code...

[Miljar]

I can't figure it out either. Thanks for updating your PR. Maybe one day we'll figure out what's wrong with the coverage ;)