Refactor: Parse return statements without an expression properly

This is an internal refactoring necessary for the Skylark linter.
It does not change any behavior.

RELNOTES: None
PiperOrigin-RevId: 166199367
diff --git a/src/test/java/com/google/devtools/build/lib/syntax/ParserTest.java b/src/test/java/com/google/devtools/build/lib/syntax/ParserTest.java
index 94cdb30..288038f 100644
--- a/src/test/java/com/google/devtools/build/lib/syntax/ParserTest.java
+++ b/src/test/java/com/google/devtools/build/lib/syntax/ParserTest.java
@@ -971,12 +971,7 @@
       assertThat(bodyNoExpr).hasSize(1);
 
       ReturnStatement returnNoExpr = (ReturnStatement) bodyNoExpr.get(0);
-      Identifier none = (Identifier) returnNoExpr.getReturnExpression();
-      assertThat(none.getName()).isEqualTo("None");
-      assertLocation(
-          returnNoExpr.getLocation().getStartOffset(),
-          returnNoExpr.getLocation().getEndOffset(),
-          none.getLocation());
+      assertThat(returnNoExpr.getReturnExpression()).isNull();
     }
   }