unit: validate valueExpression (#2396)
unit: validate valueExpression (#2396)

* check the JSON conversion with different types of input.
* validate if there is any invalid type is passed in.
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios