Fix #407 NullPointerException in Document.getProperties()
Fix #407 NullPointerException in Document.getProperties()

- check if current revision is null.
- if null, return null

couchbase/couchbase-lite-java-core,4u7/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core,gotmyjobs/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core,mariosotil/couchbase-lite-java-core,Spotme/couchbase-lite-java-core,netsense-sas/couchbase-lite-java-core