OPAL-2084: Filtering null before transforming list of variables
Merge pull request #59 from emorency/OPAL-2077

OPAL-2084: Filtering null before transforming list of variables
* Value.getValue() is never null but throws NullPointerException * Replace @Nonnull by @NotNull
* Attribute.getNamespace() is never null but throws NullPointerException
Fix PMD
Fix FindBugs
Fix warnings
Work on remove variable (OPAL-2171)
Work on remove variable (OPAL-2171)
Fix OPAL-2171: Deleting a variable in SQL, only deletes the associated values
Fix PMD warnings
Revert @OrderColumn to @IndexColumn
Use @OrderColumn instead of @IndexColumn and need to upgrade Opal DBs
Use Mongo id for variable instead of name
Upgrade to Gradle 1.10
Add error-prone during compilation
Add benchmark test
Add benchmark test
Add simple benchmark for hibernate
Clear table dbObject on drop