Remove some boxing via Optional in getResultType.

Not a big deal, but this is an extra allocation and a bit obfuscated. (I almost want a Klippy for this pattern; I've seen it in readability reviews too...)

PiperOrigin-RevId: 693353388

check_api/src/main/java/com/google/errorprone/util/ASTHelpers.java

@@ -535,7 +535,7 @@ public static Type getReturnType(ExpressionTree expressionTree) {
    */
   public static @Nullable Type getResultType(ExpressionTree expressionTree) {
     Type type = ASTHelpers.getType(expressionTree);
-    return type == null ? null : Optional.ofNullable(type.getReturnType()).orElse(type);
+    return type == null ? null : (type.getReturnType() == null ? type : type.getReturnType());
   }
 
   /**