fix(graph): check if element exists in isNode/Edge

Author: bcakmakoglu

packages/vue-flow/src/utils/graph.ts

@@ -40,11 +40,12 @@ export const getHostForElement = (element: HTMLElement): Document => {
 }
 
 type MaybeElement = Node | Edge | Connection | FlowElement
-export const isEdge = (element: MaybeElement): element is Edge => 'id' in element && 'source' in element && 'target' in element
+export const isEdge = (element: MaybeElement): element is Edge =>
+  element && 'id' in element && 'source' in element && 'target' in element
 export const isGraphEdge = (element: MaybeElement): element is GraphEdge =>
   isEdge(element) && 'sourceNode' in element && 'targetNode' in element
 
-export const isNode = (element: MaybeElement): element is Node => 'id' in element && !isEdge(element)
+export const isNode = (element: MaybeElement): element is Node => element && 'id' in element && !isEdge(element)
 export const isGraphNode = (element: MaybeElement): element is GraphNode => isNode(element) && 'computedPosition' in element
 
 export const parseNode = (node: Node, nodeExtent: CoordinateExtent, defaults?: Partial<GraphNode>): GraphNode => {