Fix to throw exception in case of empty chat template in chat scenario

src/cpp/include/openvino/genai/tokenizer.hpp

@@ -83,6 +83,12 @@ class OPENVINO_GENAI_EXPORTS Tokenizer {
                                     bool add_generation_prompt, 
                                     const std::string& chat_template="") const;
 
+    /**
+     * @brief Returns true if chat tempate exists and is ready to be applied; false otherwise
+     * @return is chat tempate ready
+     */
+    bool is_chat_template_ready() const;
+
     // information about <bos>, <eos> tokens should be public,
     // they are used at least in StreamerBase descendants
     int64_t get_bos_token_id() const;

src/cpp/src/llm_pipeline.cpp

@@ -266,11 +266,16 @@ class StatefulLLMPipeline final : public LLMPipelineImplBase {
             m_history = {};
             m_templated_chat_history = "";
         }
+        OPENVINO_ASSERT(m_tokenizer.is_chat_template_ready(),
+                        "There is no existing chat template for actual model. LLMPipeline cannot work in chat mode."
+                        " Please add chat template to tokenizer_config.json or use another model.");
+
         if (system_message.empty())
             return;
 
         m_history.push_back({{"role", "system"}, {"content", system_message}});
         constexpr bool add_generation_prompt = false;
+
         m_templated_chat_history = m_tokenizer.apply_chat_template(m_history, add_generation_prompt);
     }
 

src/cpp/src/tokenizer.cpp

@@ -434,7 +434,9 @@ class Tokenizer::TokenizerImpl {
         }
     }
 
-
+    bool is_chat_template_ready() {
+        return !m_chat_template.empty();
+    }
 };
 
 Tokenizer::Tokenizer(const std::string& tokenizer_path, const ov::AnyMap& plugin_config) {
@@ -500,6 +502,11 @@ std::string Tokenizer::apply_chat_template(ChatHistory history,
     return m_pimpl->apply_chat_template(history, add_generation_prompt, chat_template);
 }
 
+bool Tokenizer::is_chat_template_ready() const {
+    return m_pimpl->is_chat_template_ready();
+};
+
+
 Tokenizer::~Tokenizer() = default;
 }  // namespace genai
 }  // namespace ov