Separate build-specific types and types inherent to Skylark.

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MOS_MIGRATED_REVID=103374106
diff --git a/src/main/java/com/google/devtools/build/lib/packages/EnvironmentGroup.java b/src/main/java/com/google/devtools/build/lib/packages/EnvironmentGroup.java
index ff9edae..b6de272 100644
--- a/src/main/java/com/google/devtools/build/lib/packages/EnvironmentGroup.java
+++ b/src/main/java/com/google/devtools/build/lib/packages/EnvironmentGroup.java
@@ -161,7 +161,7 @@
       Target env = pkgTargets.get(envName.getName());
       if (isValidEnvironment(env, envName, "", events)) {
         AttributeMap attr = NonconfigurableAttributeMapper.of((Rule) env);
-        for (Label fulfilledEnv : attr.get("fulfills", Type.LABEL_LIST)) {
+        for (Label fulfilledEnv : attr.get("fulfills", BuildType.LABEL_LIST)) {
           if (isValidEnvironment(pkgTargets.get(fulfilledEnv.getName()), fulfilledEnv,
               "in \"fulfills\" attribute of " + envName + ": ", events)) {
             directFulfillers.put(fulfilledEnv, envName);