Supply an implementation for the DataFlowStack-required interface for `DataFlowCall`: ``` /** Gets an argument to this call as a Node. */ ArgumentNode getAnArgumentNode(){ none() } // TODO: JB1 return an argument as a DataFlow ArgumentNode /** Gets the data flow node corresponding to this call. */ ExprNode getNode() { none() } // TODO: JB1 return this Call as a Node /** Gets the target of the call, as a DataFlowCallable. */ DataFlowCallable getARuntimeTarget(){ none() } // TODO ```