datastore support set null value #295
Description
based on cloud datastore protobuf, it is possible to set null to an attribute.
currently gcloud will raise exception raise ValueError("Unknown protobuf attr type %s" % type(val)) while user trying to set null for any attribute.
// A message that can hold any of the supported value types and associated
// metadata.
//
// At most one of the <type>Value fields may be set.
// If none are set the value is "null".
//
message Value {
// ...
}