Fix segfault caused by ensuring valueless statics are not evaluated (#21577)

(cherry picked from commit c06623bf8c)

compiler/semtypinst.nim

@@ -201,7 +201,7 @@ proc hasValuelessStatics(n: PNode): bool =
     proc doThing(_: MyThing)
   ]#
   if n.safeLen == 0:
-    n.typ.kind == tyStatic
+    n.typ == nil or n.typ.kind == tyStatic
   else:
     for x in n:
       if hasValuelessStatics(x):

tests/statictypes/tstatictypes.nim

@@ -391,3 +391,23 @@ var sorted = newSeq[int](1000)
 for i in 0..<sorted.len: sorted[i] = i*2
 doAssert isSorted2(sorted, compare)
 doAssert isSorted2(sorted, proc (a, b: int): bool {.inline.} = a < b)
+
+
+block: # Ensure static descriminated objects compile
+  type
+    ObjKind = enum
+      KindA, KindB, KindC
+
+    MyObject[kind: static[ObjKind]] = object of RootObj
+      myNumber: int
+      when kind != KindA:
+        driverType: int
+        otherField: int
+      elif kind == KindC:
+        driverType: uint
+        otherField: int
+
+  var instance: MyObject[KindA]
+  discard instance
+  discard MyObject[KindC]()
+