MongoDBDataHandler.onViaEmbeddable bug with null-valued embedded field in MongoDB

MongoDBDataHandler.onViaEmbeddable should check for null before using embeddedDocumentObject because in can be null in database.
#438
#438
#436
Fixes for map also #434
Merge branch 'trunk' of github.com:impetus-opensource/Kundera into trunk
Refactoring. issue #437
Merge branch 'trunk' of github.com:impetus-opensource/Kundera into trunk
Issue #437
Merge branch 'trunk' of github.com:impetus-opensource/Kundera into trunk
Fix Issue#437
fixed npe in OneToManyRelationMetadataProcessor
Merge branch 'trunk' of github.com:trajar/Kundera into trunk