code: public boolean hasExternalProjection( String alias,
                                            String externalNodeKey ) {
          return this.snapshot.get().hasExternalProjection(alias, externalNodeKey);
      }
docs: Determine there is a projection with the given alias and projected (internal) node key
  
  @param alias the alias
  @param externalNodeKey the node key of the projected (internal) node
  @return true if there is such a projection, or false otherwise