From a62e58ce4ecaaec26f7621d705464dda527e6a84 Mon Sep 17 00:00:00 2001
From: ghm <ghm@google.com>
Date: Thu, 25 Jan 2024 03:31:39 -0800
Subject: [PATCH] Fix a crash in `UnnecessaryStringBuilder`

Fixes external #4195

PiperOrigin-RevId: 601397633
---
 .../bugpatterns/UnnecessaryStringBuilder.java       |  3 +++
 .../bugpatterns/UnnecessaryStringBuilderTest.java   | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilder.java b/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilder.java
index 57dd19f8846..c09e011b86d 100644
--- a/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilder.java
+++ b/core/src/main/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilder.java
@@ -117,6 +117,9 @@ public Description matchNewClass(NewClassTree tree, VisitorState state) {
       }
     }
     ASTHelpers.TargetType target = ASTHelpers.targetType(state.withPath(path));
+    if (target == null) {
+      return NO_MATCH;
+    }
     if (!isUsedAsStringBuilder(state, target)) {
       return describeMatch(
           path.getLeaf(), SuggestedFix.replace(path.getLeaf(), replacement(state, parts)));
diff --git a/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilderTest.java b/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilderTest.java
index a022aae7247..fc96ab21d2d 100644
--- a/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilderTest.java
+++ b/core/src/test/java/com/google/errorprone/bugpatterns/UnnecessaryStringBuilderTest.java
@@ -164,4 +164,17 @@ public void varType() {
             "}")
         .doTest();
   }
+
+  @Test
+  public void unusedReturnValue() {
+    testHelper
+        .addSourceLines(
+            "Test.java",
+            "class Test {",
+            "  void f() {",
+            "    new StringBuilder().append(\"foo\");",
+            "  }",
+            "}")
+        .doTest();
+  }
 }