message: Update graph.ts
  added check to verify handle exists in node
diff: @@ -65,10 +65,14 @@ export const addEdge = (edgeParams: Edge | Connection, elements: Elements): Elem
  throw new Error(`Can't create edge. Node with id=${id} does not exist.`);
  }
  });
  - // need to check if handles exist
  - //
  - //
  - //
  +
  + // make sure that the handles exists in each node
  + const handleElements = Array.from(document.getElementsByClassName("react-flow__handle")) as HTMLDivElement[]
  + [[edgeParams.source, edgeParams.sourceHandle], [edgeParams.target, edgeParams.targetHandle]].forEach(([nodeId, handleId]) => {
  + if (!handleElements.find((he) => he.getAttribute('data-nodeid') === nodeId && he.getAttribute('data-handleid') === handleId)) {
  + throw new Error(`Can't create edge. Handle with id=${handleId} does not exist within Node with id=${nodeId}.`);
  + }
  + })
  let edge: Edge
  if (isEdge(edgeParams)) {
  