Fix #21401 (#22232)

lib/system/seqs_v2.nim

@@ -11,6 +11,11 @@
 # import typetraits
 # strs already imported allocateds for us.
 
+
+# Some optimizations here may be not to empty-seq-initialize some symbols, then StrictNotNil complains.
+{.push warning[StrictNotNil]: off.}  # See https://github.com/nim-lang/Nim/issues/21401
+
+
 proc supportsCopyMem(t: typedesc): bool {.magic: "TypeTrait".}
 
 ## Default seq implementation used by Nim's core.
@@ -149,3 +154,6 @@ func capacity*[T](self: seq[T]): int {.inline.} =
   {.cast(noSideEffect).}:
     let sek = unsafeAddr self
     result = capacityImpl(cast[ptr NimSeqV2](sek)[])
+
+
+{.pop.}  # See https://github.com/nim-lang/Nim/issues/21401