pkg:compiler - enable and fix null operator lints

Change-Id: I5aaef20fdd61fd6ac9dc69978111fb680c7f99e5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/211624
Auto-Submit: Kevin Moore <kevmoo@google.com>
Commit-Queue: Kevin Moore <kevmoo@google.com>
Reviewed-by: Joshua Litt <joshualitt@google.com>

https://dart.googlesource.com/sdk/+/b85488cedd0a21f201a9e8b768e94ca182de0b7e
diff --git a/commits.json b/commits.json
index c08f4bf..7f26f9f 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"5f7d0053f98dd5284f69514504e8b0f318ac9f13",
   "external/github.com/flutter/flutter":"69ae50310b07f8ef80fd1f14af8209adb2b83f03",
-  "sdk":"7786183e144df65b5411163caf8abe8b7e93df62"
+  "sdk":"b85488cedd0a21f201a9e8b768e94ca182de0b7e"
 }
\ No newline at end of file