Fix issue where the Interpreter::ModifyGraphWithDelegate and

Subgraph::ModifyGraphWithDelegate methods did not specify
the behaviour when the delegate parameter is null.

PiperOrigin-RevId: 352655477
Change-Id: Ia3997ba325cb76b3c76c8672c4b6102343da8443

tensorflow/lite/core/subgraph.cc

@@ -1488,6 +1488,11 @@ TfLiteStatus Subgraph::ModifyGraphWithDelegate(TfLiteDelegate* delegate) {
   TFLITE_SCOPED_TAGGED_DEFAULT_PROFILE(profiler_.get(),
                                        "ModifyGraphWithDelegate");
 
+  if (delegate == nullptr) {
+    ReportError("Null delegate.");
+    return kTfLiteDelegateError;
+  }
+
   // Restore delegation state if applicable.
   TF_LITE_ENSURE_STATUS(RedoAllDelegates());
 

tensorflow/lite/core/subgraph.h

@@ -552,7 +552,8 @@ class Subgraph {
   // Returns one of the following status codes:
   // 1. kTfLiteOk: Delegation succeeded
   // 2. kTfLiteDelegateError: Delegation failed due to an error *in the
-  // delegate*. The Subgraph has been restored to its pre-delegation state.
+  // delegate*, or the delegate parameter was null. The Subgraph has been
+  // restored to its pre-delegation state.
   // NOTE: This reverts all delegates previously applied to the Subgraph.
   // 3. kTfLiteApplicationError : Delegation failed to be applied due to the
   // incompatibility with the TfLite runtime, e.g., the model graph is already

tensorflow/lite/delegates/delegate_test.cc

@@ -42,6 +42,11 @@ using test_utils::TestFP16Delegation;
 
 namespace {
 
+TEST_F(TestDelegate, NullDelegate) {
+  EXPECT_EQ(interpreter_->ModifyGraphWithDelegate(nullptr),
+            kTfLiteDelegateError);
+}
+
 TEST_F(TestDelegate, BasicDelegate) {
   delegate_ = std::unique_ptr<SimpleDelegate>(new SimpleDelegate({0, 1, 2}));
   interpreter_->ModifyGraphWithDelegate(delegate_->get_tf_lite_delegate());
@@ -916,6 +921,14 @@ TEST_P(TestFP16Delegation, NonDelegatedInterpreterWorks) {
   VerifyInvoke();
 }
 
+TEST_F(TestFP16Delegation, NullDelegate) {
+  EXPECT_EQ(interpreter_->ModifyGraphWithDelegate(nullptr),
+            kTfLiteDelegateError);
+  // Verify that resulting interpreter still works, despite null delegate.
+  ASSERT_EQ(interpreter_->AllocateTensors(), kTfLiteOk);
+  VerifyInvoke();
+}
+
 TEST_P(TestFP16Delegation, DelegationWorks) {
   delegate_ = std::unique_ptr<FP16Delegate>(
       new FP16Delegate(/**num_delegated_subsets**/ GetParam()));

tensorflow/lite/interpreter.h

@@ -469,7 +469,8 @@ class Interpreter {
   /// Returns one of the following four status codes:
   /// 1. kTfLiteOk: Success.
   /// 2. kTfLiteDelegateError: Delegation failed due to an error in the
-  /// delegate. The Interpreter has been restored to its pre-delegation state.
+  /// delegate, or the delegate parameter was null. The Interpreter has been
+  /// restored to its pre-delegation state.
   /// NOTE: This undoes all delegates previously applied to the Interpreter.
   /// 3. kTfLiteApplicationError : Delegation failed to be applied due to the
   /// incompatibility with the TfLite runtime, e.g., the model graph is already