From 27f21d4d13075e33fecc86e88b43fe9b192e4235 Mon Sep 17 00:00:00 2001
From: Piotr Wilkin <ilintar@gmail.com>
Date: Fri, 23 Jan 2026 20:18:25 +0100
Subject: [PATCH] Add workaround for templates requiring non-null content

---
 common/chat.cpp       | 13 ++++++++
 common/jinja/caps.cpp | 70 ++++++++++++++++++++++++++++++++++++++++---
 common/jinja/caps.h   |  1 +
 3 files changed, 80 insertions(+), 4 deletions(-)

diff --git a/common/chat.cpp b/common/chat.cpp
index 2bf4632669..b0bc187a7d 100644
--- a/common/chat.cpp
+++ b/common/chat.cpp
@@ -2929,6 +2929,15 @@ static void system_message_not_supported(json & messages) {
     }
 }
 
+static void requires_non_null_content(json & messages) {
+    GGML_ASSERT(messages.is_array());
+    for (auto & message : messages) {
+        if (message.contains("tool_calls") && !messages.contains("content")) {
+            messages["content"] = "";
+        }
+    }
+}
+
 static void func_args_not_string(json & messages) {
     GGML_ASSERT(messages.is_array());
     for (auto & message : messages) {
@@ -3034,6 +3043,10 @@ static common_chat_params common_chat_templates_apply_jinja(
         workaround::system_message_not_supported(params.messages);
     }
 
+    if (!tmpl.original_caps().requires_non_null_content) {
+        workaround::requires_non_null_content(params.messages);
+    }
+
     params.extra_context = json::object();
     for (auto el : inputs.chat_template_kwargs) {
         params.extra_context[el.first] = json::parse(el.second);
diff --git a/common/jinja/caps.cpp b/common/jinja/caps.cpp
index f27490f1fb..ec8509785e 100644
--- a/common/jinja/caps.cpp
+++ b/common/jinja/caps.cpp
@@ -64,6 +64,7 @@ static void caps_print_stats(value & v, const std::string & path) {
 std::map<std::string, bool> caps::to_map() const {
     return {
         {"requires_typed_content", requires_typed_content},
+        {"requires_non_null_content", requires_non_null_content},
         {"supports_tools", supports_tools},
         {"supports_tool_calls", supports_tool_calls},
         {"supports_parallel_tool_calls", supports_parallel_tool_calls},
@@ -160,7 +161,7 @@ caps caps_get(jinja::program & prog) {
                     {"content", "Assistant message"},
                     {"tool_calls", json::array({
                         {
-                            {"id", "call1"},
+                            {"id", "call0001"},
                             {"type", "function"},
                             {"function", {
                                 {"name", "tool1"},
@@ -170,10 +171,10 @@ caps caps_get(jinja::program & prog) {
                             }}
                         },
                         {
-                            {"id", "call2"},
+                            {"id", "call0002"},
                             {"type", "function"},
                             {"function", {
-                                {"name", "tool2"},
+                                {"name", "tool1"},
                                 {"arguments", {
                                     {"arg", "value"}
                                 }}
@@ -194,7 +195,7 @@ caps caps_get(jinja::program & prog) {
                     {"name", "tool"},
                     {"type", "function"},
                     {"function", {
-                        {"name", "tool"},
+                        {"name", "tool1"},
                         {"description", "Tool description"},
                         {"parameters", {
                             {"type", "object"},
@@ -238,6 +239,67 @@ caps caps_get(jinja::program & prog) {
         }
     );
 
+    // case: requires non-null content in tool calls
+    caps_try_execute(
+        prog,
+        [&]() {
+            // messages
+            return json::array({
+                {
+                    {"role", "user"},
+                    {"content", "User message"},
+                },
+                {
+                    {"role", "assistant"},
+                    {"tool_calls", json::array({
+                        {
+                            {"id", "call0001"},
+                            {"type", "function"},
+                            {"function", {
+                                {"name", "tool1"},
+                                {"arguments", {
+                                    {"arg", "value"}
+                                }}
+                            }}
+                        },
+                    })}
+                },
+                {
+                    {"role", "user"},
+                    {"content", "User message"},
+                },
+            });
+        },
+        [&]() {
+            // tools
+            return json::array({
+                {
+                    {"name", "tool"},
+                    {"type", "function"},
+                    {"function", {
+                        {"name", "tool1"},
+                        {"description", "Tool description"},
+                        {"parameters", {
+                            {"type", "object"},
+                            {"properties", {
+                                {"arg", {
+                                    {"type", "string"},
+                                    {"description", "Arg description"},
+                                }},
+                            }},
+                            {"required", json::array({ "arg" })},
+                        }},
+                    }},
+                },
+            });
+        },
+        [&](bool success, value & messages, value & tools) {
+            if (!success) {
+                result.requires_non_null_content = true;
+            }
+        }
+    );
+
     // case: preserve reasoning content in chat history
     caps_try_execute(
         prog,
diff --git a/common/jinja/caps.h b/common/jinja/caps.h
index 77df117baa..c077ed49e6 100644
--- a/common/jinja/caps.h
+++ b/common/jinja/caps.h
@@ -15,6 +15,7 @@ struct caps {
     bool supports_preserve_reasoning = false; // support assistant message with reasoning_content
 
     bool requires_typed_content = false; // default: use string content
+    bool requires_non_null_content = false; // requires "" instead of null for content in tool calls
 
     // for reporting on server
     std::map<std::string, bool> to_map() const;