code: public GroovyExpression generateAdjacentVerticesExpression(GroovyExpression parent, AtlasEdgeDirection dir,
              String label) {
          return new FunctionCallExpression(TraversalStepType.FLAT_MAP_TO_ELEMENTS, parent, getGremlinFunctionName(dir), new LiteralExpression(label));
      }
docs: Generates an expression that gets the vertices adjacent to the vertex in 'parent'
  in the specified direction, following only edges with the given label.
  
  @param parent
  @param dir
  @return