diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueImmutableFields.java b/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueImmutableFields.java
index <HASH>..<HASH> 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueImmutableFields.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/AutoValueImmutableFields.java
@@ -51,7 +51,7 @@ import javax.lang.model.element.Modifier;
 public class AutoValueImmutableFields extends BugChecker implements ClassTreeMatcher {
 
   private static final String MESSAGE =
-      "AutoValue instances should be deeply immutable. Therefore, we recommend returning a %s "
+      "AutoValue instances should be deeply immutable. Therefore, we recommend returning %s "
           + "instead. Read more at "
           + "http://goo.gl/qWo9sC"
       ;
Remove an unnecessary indefinite article.

As it stands, this produces messages like this:
"AutoValue instances should be deeply immutable. Therefore, we recommend returning a ImmutableMap instead." Saying "...return ImmutableMap" reads just as well in addition to being grammatically correct.

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Created by MOE: <URL>