public Builder edgeDirection(final Direction direction) {
            if (null == direction) throw Graph.Exceptions.argumentCanNotBeNull("direction");
            return edgeTraversal(__.toE(direction));
        }
Move any valid path into the VP's memory.
@param vertex The current vertex.
@param memory The VertexProgram's memory.
gremlin-core/src/main/java/org/apache/tinkerpop/gremlin/process/computer/search/path/ShortestPathVertexProgram.java