Fix undefined behavior in `tf.raw_ops.Switch` in eager mode.

PiperOrigin-RevId: 332578058
Change-Id: I9727571d2f21476b10d8aa27c1b7176564b76ac9

tensorflow/core/common_runtime/eager/kernel_and_device.cc

@@ -304,7 +304,12 @@ Status KernelAndDeviceOp::Run(
   if (outputs != nullptr) {
     outputs->clear();
     for (int i = 0; i < context.num_outputs(); ++i) {
-      outputs->push_back(Tensor(*context.mutable_output(i)));
+      const auto* output_tensor = context.mutable_output(i);
+      if (output_tensor != nullptr) {
+        outputs->push_back(Tensor(*output_tensor));
+      } else {
+        outputs->push_back(Tensor());
+      }
     }
   }
   return Status::OK();

tensorflow/python/kernel_tests/control_flow_ops_py_test.py

@@ -4554,6 +4554,14 @@ class ControlFlowTest(test.TestCase, parameterized.TestCase):
       result = control_flow_ops.merge([v_f, v_t])
       self.evaluate(result)
 
+  def testSwitchEagerMode(self):
+    if not context.executing_eagerly():
+      return
+    input_data = [1, 2, 3, 4]
+    vf, vt = control_flow_ops.switch(input_data, False)
+    self.assertAllEqual(vf, input_data)
+    self.assertAllEqual(vt, [])
+
   @test_util.run_deprecated_v1
   def testQIntArgAndRet(self):