Handle null bos and eos token (#66)

Author: jackzhxng

src/hf_tokenizer.cpp

@@ -142,8 +142,15 @@ Error HFTokenizer::load(const std::string& path) {
 
     // Pull out the token strings
     try {
-      const std::string bos_token = parsed_config_json.at("bos_token");
-      const std::string eos_token = parsed_config_json.at("eos_token");
+      const std::string bos_token =
+	  parsed_config_json.contains("bos_token") && !parsed_config_json["bos_token"].is_null()
+	  ? parsed_config_json["bos_token"].get<std::string>()
+	  : "";
+
+      const std::string eos_token =
+	  parsed_config_json.contains("eos_token") && !parsed_config_json["eos_token"].is_null()
+	  ? parsed_config_json["eos_token"].get<std::string>()
+	  : "";
       const auto bos_res = special_token_map_->tryGetInteger(bos_token);
       const auto eos_res = special_token_map_->tryGetInteger(eos_token);
       if (!bos_res) {