question: public Optional < BlazeVertex > vertex ( final String vertexId ) { try ( final CloseableIterator < Vertex > it = vertices ( vertexId ) ) { final Optional < BlazeVertex > v = it . hasNext ( ) ? Optional . of ( ( BlazeVertex ) it . next ( ) ) : Optional . empty ( ) ; if ( it . hasNext ( ) ) { throw new IllegalStateException ( "Multiple vertices found with id: " + vertexId ) ; } return v ; } }
target:  Lookup a vertex by id.