Make sure disabled FDO features are filtered out.

Without this, the FDO features enabled under --fdo* blaze options are not removed when BUILD files contain "features = ['-fdo_instrument', '-fdo_optimize']".

--
MOS_MIGRATED_REVID=103431508
diff --git a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
index 2f44210..479b0b5 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/RuleClass.java
@@ -1295,7 +1295,8 @@
     }
 
     String name = fragmentNameResolver.resolveName(configurationFragment);
-    return (name != null && requiredConfigurationFragmentNames.get(config).contains(name));
+    ImmutableSet<String> fragmentNames = requiredConfigurationFragmentNames.get(config);
+    return (name != null && fragmentNames != null && fragmentNames.contains(name));
   }
 
   /**