Avoid resetting ArtifactNestedSetFunction too often.

RELNOTES: None
PiperOrigin-RevId: 292409117
diff --git a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetFunction.java b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetFunction.java
index df85456..47409ae 100644
--- a/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetFunction.java
+++ b/src/main/java/com/google/devtools/build/lib/skyframe/ArtifactNestedSetFunction.java
@@ -99,9 +99,6 @@
                 artifactNestedSetKey.directKeys(),
                 IOException.class,
                 ActionExecutionException.class);
-    if (env.valuesMissing()) {
-      return null;
-    }
 
     // Evaluate all children.
     ArrayList<SkyKey> transitiveKeys = new ArrayList<>();