SelectorProvider CLIENT implementation shows extra blank entry in ListBox

Note: Please see comment below - this may not be a bug

Found in Stunner BPMN implementation. When a form property has a REMOTE SelectorProvider implementation, the ListBox in the UI shows a single empty entry, but when a CLIENT implementation is provided, there are 2 empty entries, where there should only be one.

This problem was found in the implementation of the DefaultRoute property of ExclusiveDatabasedGateway in Stunner. See
https://github.com/kiegroup/kie-wb-common/blob/master/kie-wb-common-stunner/kie-wb-common-stunner-sets/kie-wb-common-stunner-bpmn/kie-wb-common-stunner-bpmn-api/src/main/java/org/kie/workbench/common/stunner/bpmn/definition/property/gateway/ExclusiveGatewayExecutionSet.java#L50