fixes #6555

compiler/sempass2.nim

@@ -518,6 +518,7 @@ proc notNilCheck(tracked: PEffects, n: PNode, paramType: PType) =
     procVarcheck skipConvAndClosure(n)
   #elif n.kind in nkSymChoices:
   #  echo "came here"
+  let paramType = paramType.skipTypesOrNil(abstractInst)
   if paramType != nil and tfNotNil in paramType.flags and
       n.typ != nil and tfNotNil notin n.typ.flags:
     if n.kind == nkAddr:

tests/notnil/tmust_compile.nim

@@ -24,3 +24,14 @@ var b = Obj() # this doesn't (also doesn't works with additional fields)
 var z = Obj2[int]()
 
 echo "success"
+
+# bug #6555
+
+import tables
+
+type
+  TaskOrNil = ref object
+  Task = TaskOrNil not nil
+
+let table = newTable[string, Task]()
+table.del("task")