ImpossibleNullComparison: emit empty fixes.

There's a subtle logic error here: empty fixes are meant to be emitted, there's just no fix.

PiperOrigin-RevId: 610434295

Author: graememorgan

core/src/main/java/com/google/errorprone/bugpatterns/ImpossibleNullComparison.java

@@ -144,11 +144,13 @@ private static boolean isNull(ExpressionTree tree) {
               "com.google.protobuf.GeneratedMessageLite", "com.google.protobuf.GeneratedMessage");
 
   private final boolean matchTestAssertions;
+  private final boolean emitEmptyFixes;
 
   @Inject
   ImpossibleNullComparison(ErrorProneFlags flags) {
     this.matchTestAssertions =
         flags.getBoolean("ProtoFieldNullComparison:MatchTestAssertions").orElse(true);
+    this.emitEmptyFixes = flags.getBoolean("ImmutableNullComparison:EmitEmptyFixes").orElse(true);
   }
 
   @Override
@@ -248,7 +250,7 @@ public Void visitMethodInvocation(MethodInvocationTree node, Void unused) {
       }
       getFixer(argument, subState)
           .map(f -> problemType.fix(f, node, subState))
-          .filter(f -> !f.isEmpty())
+          .filter(f -> emitEmptyFixes || !f.isEmpty())
           .map(f -> describeMatch(node, f))
           .ifPresent(state::reportMatch);
 

core/src/test/java/com/google/errorprone/bugpatterns/ImpossibleNullComparisonTest.java

@@ -173,12 +173,15 @@ public void extendableMessageGetExtension1param() {
     compilationHelper
         .addSourceLines(
             "Test.java",
+            "import static org.junit.Assert.assertNotNull;",
             "import com.google.protobuf.ExtensionLite;",
             "import com.google.errorprone.bugpatterns.proto.ProtoTest.TestProtoMessage;",
             "public class Test {",
             "  public void test(TestProtoMessage e, ExtensionLite extensionLite) {",
             "    // BUG: Diagnostic contains:",
             "    boolean a = e.getExtension(extensionLite) == null;",
+            "    // BUG: Diagnostic contains:",
+            "    assertNotNull(e.getExtension(extensionLite));",
             "  }",
             "}")
         .doTest();