fix: nil-safe content.strip in chat_completion final-response paths

CHANGELOG.md

@@ -1,3 +1,8 @@
+## [Unreleased]
+
+### Fixed
+- `NoMethodError: undefined method 'strip' for nil` in `Raix::ChatCompletion` when an LLM (notably Gemini under certain stop conditions) returns a final assistant message with `"content": null`. Three call sites in `lib/raix/chat_completion.rb` now use `content.to_s.strip` so a nil response coerces to `""` instead of raising.
+
 ## [2.0.2] - 2026-03-27
 
 ### Fixed

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    raix (2.0.1)
+    raix (2.0.2)
       activesupport (>= 6.0)
       faraday-retry (~> 2.0)
       ostruct
@@ -49,8 +49,8 @@ GEM
       net-http
     faraday-retry (2.4.0)
       faraday (~> 2.0)
-    ffi (1.17.2)
     ffi (1.17.2-arm64-darwin)
+    ffi (1.17.2-x86_64-linux-gnu)
     formatador (1.1.0)
     guard (2.18.1)
       formatador (>= 0.2.4)
@@ -83,18 +83,16 @@ GEM
     lumberjack (1.2.10)
     marcel (1.1.0)
     method_source (1.1.0)
-    mini_portile2 (2.8.9)
     minitest (5.27.0)
     multipart-post (2.4.1)
     nenv (0.3.0)
     net-http (0.4.1)
       uri
     netrc (0.11.0)
-    nokogiri (1.18.8)
-      mini_portile2 (~> 2.8.2)
-      racc (~> 1.4)
     nokogiri (1.18.8-arm64-darwin)
       racc (~> 1.4)
+    nokogiri (1.18.8-x86_64-linux-gnu)
+      racc (~> 1.4)
     notiffany (0.1.3)
       nenv (~> 0.1)
       shellany (~> 0.0)

lib/raix/chat_completion.rb

@@ -174,7 +174,7 @@ def chat_completion(params: {}, loop: false, json: false, raw: false, openai: ni
             # Process the final response
             content = response.dig("choices", 0, "message", "content")
             transcript << { assistant: content } if save_response
-            return raw ? response : content.strip
+            return raw ? response : content.to_s.strip
           end
 
           # Dispatch tool calls
@@ -215,15 +215,15 @@ def chat_completion(params: {}, loop: false, json: false, raw: false, openai: ni
 
             content = response.dig("choices", 0, "message", "content")
             transcript << { assistant: content } if save_response
-            return raw ? response : content.strip
+            return raw ? response : content.to_s.strip
           end
         end
 
         response.tap do |res|
           content = res.dig("choices", 0, "message", "content")
 
           transcript << { assistant: content } if save_response
-          content = content.strip
+          content = content.to_s.strip
 
           if json
             # Make automatic JSON parsing available to non-OpenAI providers that don't support the response_format parameter

spec/raix/nil_content_spec.rb

@@ -0,0 +1,183 @@
+# frozen_string_literal: true
+
+RSpec.describe "nil content in final assistant response" do
+  # Some providers (notably Gemini under certain stop conditions) return a final
+  # assistant message with `content: nil`. The three call sites in chat_completion
+  # that turn the response into a string previously crashed with NoMethodError on
+  # `nil.strip`. They now use `content.to_s.strip` and should return "".
+
+  def nil_content_response(tool_calls: nil)
+    {
+      "choices" => [
+        {
+          "message" => {
+            "role" => "assistant",
+            "content" => nil,
+            "tool_calls" => tool_calls
+          },
+          "finish_reason" => tool_calls ? "tool_calls" : "stop"
+        }
+      ],
+      "usage" => {
+        "prompt_tokens" => 1,
+        "completion_tokens" => 0,
+        "total_tokens" => 1
+      }
+    }
+  end
+
+  def tool_call_response
+    {
+      "choices" => [
+        {
+          "message" => {
+            "role" => "assistant",
+            "content" => nil,
+            "tool_calls" => [
+              {
+                "id" => "call_1",
+                "type" => "function",
+                "function" => {
+                  "name" => "do_thing",
+                  "arguments" => "{}"
+                }
+              }
+            ]
+          },
+          "finish_reason" => "tool_calls"
+        }
+      ],
+      "usage" => {
+        "prompt_tokens" => 1,
+        "completion_tokens" => 0,
+        "total_tokens" => 1
+      }
+    }
+  end
+
+  describe "plain final response with nil content" do
+    let(:chat_class) do
+      Class.new do
+        include Raix::ChatCompletion
+
+        def initialize
+          self.model = "test-model"
+          transcript << { user: "Hello" }
+        end
+      end
+    end
+
+    it "returns an empty string instead of raising NoMethodError" do
+      instance = chat_class.new
+      allow(instance).to receive(:ruby_llm_request).and_return(nil_content_response)
+
+      expect { instance.chat_completion }.not_to raise_error
+    end
+
+    it "returns an empty string when content is nil" do
+      instance = chat_class.new
+      allow(instance).to receive(:ruby_llm_request).and_return(nil_content_response)
+
+      expect(instance.chat_completion).to eq("")
+    end
+  end
+
+  describe "max_tool_calls exceeded with nil content on forced final response" do
+    let(:chat_class) do
+      Class.new do
+        include Raix::ChatCompletion
+        include Raix::FunctionDispatch
+
+        function :do_thing, "Does a thing" do |_arguments|
+          "done"
+        end
+
+        def initialize
+          self.model = "test-model"
+          transcript << { user: "Call do_thing repeatedly" }
+        end
+      end
+    end
+
+    it "returns an empty string instead of raising NoMethodError" do
+      instance = chat_class.new
+
+      # First call returns a tool call (which exceeds max_tool_calls=0),
+      # forcing chat_completion into the max-tool-calls-exceeded branch.
+      # The forced final response then returns nil content.
+      call_count = 0
+      allow(instance).to receive(:ruby_llm_request) do
+        call_count += 1
+        call_count == 1 ? tool_call_response : nil_content_response
+      end
+
+      expect { instance.chat_completion(max_tool_calls: 0) }.not_to raise_error
+    end
+
+    it "returns an empty string when forced final content is nil" do
+      instance = chat_class.new
+
+      call_count = 0
+      allow(instance).to receive(:ruby_llm_request) do
+        call_count += 1
+        call_count == 1 ? tool_call_response : nil_content_response
+      end
+
+      expect(instance.chat_completion(max_tool_calls: 0)).to eq("")
+    end
+  end
+
+  describe "stop_tool_calls_and_respond! with nil content on forced final response" do
+    let(:chat_class) do
+      Class.new do
+        include Raix::ChatCompletion
+        include Raix::FunctionDispatch
+
+        function :stop_now, "Halts and forces a final response" do |_arguments|
+          stop_tool_calls_and_respond!
+          "stopping"
+        end
+
+        def initialize
+          self.model = "test-model"
+          transcript << { user: "Call stop_now" }
+        end
+      end
+    end
+
+    it "returns an empty string instead of raising NoMethodError" do
+      instance = chat_class.new
+
+      stop_tool_call = {
+        "choices" => [
+          {
+            "message" => {
+              "role" => "assistant",
+              "content" => nil,
+              "tool_calls" => [
+                {
+                  "id" => "call_stop",
+                  "type" => "function",
+                  "function" => {
+                    "name" => "stop_now",
+                    "arguments" => "{}"
+                  }
+                }
+              ]
+            },
+            "finish_reason" => "tool_calls"
+          }
+        ],
+        "usage" => { "prompt_tokens" => 1, "completion_tokens" => 0, "total_tokens" => 1 }
+      }
+
+      call_count = 0
+      allow(instance).to receive(:ruby_llm_request) do
+        call_count += 1
+        call_count == 1 ? stop_tool_call : nil_content_response
+      end
+
+      expect { instance.chat_completion }.not_to raise_error
+    end
+  end
+end