update(types): Connection target and source as non-nullable strings

* Required for a valid edge, so it should be required in a connection as well

package/src/composables/useHandle.ts

@@ -26,7 +26,7 @@ export const checkElementBelowIsValid = (
   const result: Result = {
     elementBelow,
     isValid: false,
-    connection: { source: null, target: null, sourceHandle: null, targetHandle: null },
+    connection: { source: '', target: '', sourceHandle: null, targetHandle: null },
     isHoveringHandle: false,
   }
 
@@ -55,7 +55,7 @@ export const checkElementBelowIsValid = (
           }
 
       result.connection = connection
-      result.isValid = isValidConnection(connection)
+      result.isValid = isValidConnection(connection) || !result.connection.target || !result.connection.source
     }
   }
 

package/src/types/connection.ts

@@ -14,9 +14,9 @@ export enum ConnectionLineType {
 /** Connection params that are passed when onConnect is called */
 export interface Connection {
   /** Source node id */
-  source: string | null
+  source: string
   /** Target node id */
-  target: string | null
+  target: string
   /** Source handle id */
   sourceHandle: string | null
   /** Target handle id */