MODE-2185 Fixed JavaDoc error and Java compiler warnings
MODE-2178 Added test that verifies that the existing behavior works as expected

Using a criteria "... WHERE [car:engine] == '' ..." will only work when the property value
is non-null and is an empty string. This works as expected.
Merge pull request #1216 from rhauch/mode-2178

MODE-2178 Added test that verifies that the existing behavior works as expected