src: fix debug crash handling null strings

When internal debug is enabled, output null strings as
"(null)" rather than crashing, matching glibc's behavior.

PR-URL: #31523
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: rustyconover

src/debug_utils-inl.h

@@ -21,7 +21,9 @@ struct ToStringHelper {
                 enable_if<std::is_arithmetic<T>::value, bool>::type,
             typename dummy = bool>
   static std::string Convert(const T& value) { return std::to_string(value); }
-  static std::string Convert(const char* value) { return value; }
+  static std::string Convert(const char* value) {
+    return value != nullptr ? value : "(null)";
+  }
   static std::string Convert(const std::string& value) { return value; }
   static std::string Convert(bool value) { return value ? "true" : "false"; }
 };

test/cctest/test_util.cc

@@ -281,6 +281,7 @@ TEST(UtilTest, SPrintF) {
   const char* bar = "bar";
   EXPECT_EQ(SPrintF("%s %s", foo, "bar"), "foo bar");
   EXPECT_EQ(SPrintF("%s %s", foo, bar), "foo bar");
+  EXPECT_EQ(SPrintF("%s", nullptr), "(null)");
 
   EXPECT_EQ(SPrintF("[%% %s %%]", foo), "[% foo %]");