fix(core): use null as fallback id for edge source handle (#1794)

* fix(core): use null as fallback id for edge source handle

Signed-off-by: braks <78412429+bcakmakoglu@users.noreply.github.com>

* chore(changeset): add

Signed-off-by: braks <78412429+bcakmakoglu@users.noreply.github.com>

---------

Signed-off-by: braks <78412429+bcakmakoglu@users.noreply.github.com>

Author: bcakmakoglu

.changeset/cuddly-bugs-switch.md

@@ -0,0 +1,5 @@
+---
+"@vue-flow/core": patch
+---
+
+Use null as fallback id for edge source handle

packages/core/src/components/Edges/EdgeWrapper.ts

@@ -313,7 +313,7 @@ const EdgeWrapper = defineComponent({
       updating.value = true
 
       nodeId.value = isSourceHandle ? edge.value.target : edge.value.source
-      handleId.value = (isSourceHandle ? edge.value.targetHandle : edge.value.sourceHandle) ?? ''
+      handleId.value = (isSourceHandle ? edge.value.targetHandle : edge.value.sourceHandle) ?? null
 
       edgeUpdaterType.value = isSourceHandle ? 'target' : 'source'