message: Always provide std-namespace when using nullptr_t.
diff: @@ -1227,7 +1227,7 @@ TEST(CheckSymbolAsLeafTest, NotLeaf) {
  }
  TEST(CheckOptionalSymbolAsLeafTest, Nullptr) {
  - constexpr nullptr_t n = nullptr;
  + constexpr std::nullptr_t n = nullptr;
  EXPECT_EQ(CheckOptionalSymbolAsLeaf(n, FakeEnum::kZero), nullptr);
  }
  @@ -1262,7 +1262,7 @@ TEST(CheckOptionalSymbolAsLeafTest, NotLeaf) {
  }
  TEST(CheckOptionalSymbolAsNodeTest, Nullptr) {
  - constexpr nullptr_t n = nullptr;
  + constexpr std::nullptr_t n = nullptr;
  EXPECT_EQ(CheckOptionalSymbolAsNode(n, FakeEnum::kZero), nullptr);
  }
  