Stop trying to override the top level of an empty nullability vector.

PiperOrigin-RevId: 578238245
Change-Id: I87c9a059e0ec2b58651019fcefd9a197c68f37d1
diff --git a/nullability/inference/collect_evidence_test.cc b/nullability/inference/collect_evidence_test.cc
index 7ec9411..814ee15 100644
--- a/nullability/inference/collect_evidence_test.cc
+++ b/nullability/inference/collect_evidence_test.cc
@@ -463,6 +463,14 @@
                                 functionNamed("target"))));
 }
 
+// A crash repro involving callable parameters.
+TEST(CollectEvidenceFromImplementationTest, FunctionPointerParam) {
+  static constexpr llvm::StringRef Src = R"cc(
+    void target(void (*f)()) { f(); }
+  )cc";
+  EXPECT_THAT(collectEvidenceFromTargetFunction(Src), IsEmpty());
+}
+
 TEST(CollectEvidenceFromImplementationTest, NotInferenceTarget) {
   static constexpr llvm::StringRef Src = R"cc(
     template <typename T>