Enable metalava feature flag for updating Kotlin nulls

Bug: 309149849
Test: presubmit
Change-Id: I5ab071b13b25b5d9db690053d24dc543f854a92b
Merged-In: I5ab071b13b25b5d9db690053d24dc543f854a92b
diff --git a/buildSrc/private/src/main/kotlin/androidx/build/metalava/MetalavaRunner.kt b/buildSrc/private/src/main/kotlin/androidx/build/metalava/MetalavaRunner.kt
index 3c98b3e..17d8170 100644
--- a/buildSrc/private/src/main/kotlin/androidx/build/metalava/MetalavaRunner.kt
+++ b/buildSrc/private/src/main/kotlin/androidx/build/metalava/MetalavaRunner.kt
@@ -48,6 +48,7 @@
     val allArgs =
         args +
             listOf(
+                "--update-kotlin-nulls", // b/309149849: temporary feature flag
                 "--hide",
                 "HiddenSuperclass", // We allow having a hidden parent class
                 "--hide",