diff --git a/agentscope-core/src/main/java/io/agentscope/core/model/ChatModelBase.java b/agentscope-core/src/main/java/io/agentscope/core/model/ChatModelBase.java
index 271bc800a6..4e37e7db07 100644
--- a/agentscope-core/src/main/java/io/agentscope/core/model/ChatModelBase.java
+++ b/agentscope-core/src/main/java/io/agentscope/core/model/ChatModelBase.java
@@ -42,9 +42,15 @@ public abstract class ChatModelBase implements Model {
     @Override
     public final Flux<ChatResponse> stream(
             List<Msg> messages, List<ToolSchema> tools, GenerateOptions options) {
+        GenerateOptions effectiveOptions =
+                options != null ? options : GenerateOptions.builder().build();
         return TracerRegistry.get()
                 .callModel(
-                        this, messages, tools, options, () -> doStream(messages, tools, options));
+                        this,
+                        messages,
+                        tools,
+                        effectiveOptions,
+                        () -> doStream(messages, tools, effectiveOptions));
     }
 
     /**
diff --git a/agentscope-core/src/main/java/io/agentscope/core/model/OllamaChatModel.java b/agentscope-core/src/main/java/io/agentscope/core/model/OllamaChatModel.java
index 6a5ea2848e..dd8706dcf5 100644
--- a/agentscope-core/src/main/java/io/agentscope/core/model/OllamaChatModel.java
+++ b/agentscope-core/src/main/java/io/agentscope/core/model/OllamaChatModel.java
@@ -138,11 +138,13 @@ public ChatResponse chat(List<Msg> messages, GenerateOptions options) {
     @Override
     protected Flux<ChatResponse> doStream(
             List<Msg> messages, List<ToolSchema> tools, GenerateOptions options) {
+        GenerateOptions effectiveOptions =
+                options != null ? options : GenerateOptions.builder().build();
         return streamWithHttpClient(
                 messages,
                 tools,
-                options.getToolChoice(),
-                OllamaOptions.fromGenerateOptions(options),
+                effectiveOptions.getToolChoice(),
+                OllamaOptions.fromGenerateOptions(effectiveOptions),
                 true);
     }
 
diff --git a/agentscope-core/src/test/java/io/agentscope/core/model/ChatModelBaseNullOptionsTest.java b/agentscope-core/src/test/java/io/agentscope/core/model/ChatModelBaseNullOptionsTest.java
new file mode 100644
index 0000000000..bad0d8ede1
--- /dev/null
+++ b/agentscope-core/src/test/java/io/agentscope/core/model/ChatModelBaseNullOptionsTest.java
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2024-2026 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package io.agentscope.core.model;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+
+import io.agentscope.core.message.Msg;
+import io.agentscope.core.message.TextBlock;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import reactor.core.publisher.Flux;
+
+/** Tests for ChatModelBase null-safety when GenerateOptions is not provided. */
+@DisplayName("ChatModelBase Null GenerateOptions Tests")
+class ChatModelBaseNullOptionsTest {
+
+    /** A minimal ChatModelBase that captures the options passed to doStream. */
+    private static final class StubModel extends ChatModelBase {
+
+        private final AtomicReference<GenerateOptions> capturedOptions = new AtomicReference<>();
+
+        @Override
+        protected Flux<ChatResponse> doStream(
+                List<Msg> messages, List<ToolSchema> tools, GenerateOptions options) {
+            capturedOptions.set(options);
+            ChatResponse response =
+                    ChatResponse.builder()
+                            .content(List.of(TextBlock.builder().text("ok").build()))
+                            .build();
+            return Flux.just(response);
+        }
+
+        @Override
+        public String getModelName() {
+            return "stub";
+        }
+
+        GenerateOptions getCapturedOptions() {
+            return capturedOptions.get();
+        }
+    }
+
+    @Test
+    @DisplayName("stream() with null options should not throw NPE")
+    void streamWithNullOptionsShouldNotThrowNPE() {
+        StubModel model = new StubModel();
+
+        // This used to throw NPE inside OllamaChatModel.doStream() etc.
+        // ChatModelBase.stream() should now replace null with a default instance.
+        Flux<ChatResponse> flux = model.stream(List.of(), null, null);
+
+        // Subscribe to trigger the flux
+        ChatResponse response = flux.blockLast();
+        assertNotNull(response);
+
+        // Verify the options passed to doStream are non-null
+        GenerateOptions captured = model.getCapturedOptions();
+        assertNotNull(captured, "doStream should receive non-null options");
+    }
+
+    @Test
+    @DisplayName("stream() with null options should pass default GenerateOptions to doStream")
+    void streamWithNullOptionsShouldPassDefaultOptions() {
+        StubModel model = new StubModel();
+
+        model.stream(List.of(), null, null).blockLast();
+
+        GenerateOptions captured = model.getCapturedOptions();
+        assertNotNull(captured);
+        // Default options should have null fields (not throwing NPE on access)
+        assertNull(captured.getToolChoice());
+        assertNull(captured.getTemperature());
+    }
+
+    @Test
+    @DisplayName("stream() with non-null options should pass them through unchanged")
+    void streamWithNonNullOptionsShouldPassThemThrough() {
+        StubModel model = new StubModel();
+        GenerateOptions customOptions =
+                GenerateOptions.builder().temperature(0.5).maxTokens(100).build();
+
+        model.stream(List.of(), null, customOptions).blockLast();
+
+        GenerateOptions captured = model.getCapturedOptions();
+        assertNotNull(captured);
+        assertNotNull(captured.getTemperature());
+    }
+}