fix(msg):msg constructor method throw npe (#407)

Author: chiangzeon

agentscope-core/src/main/java/io/agentscope/core/message/Msg.java

@@ -27,6 +27,7 @@
 import java.time.Instant;
 import java.time.ZoneId;
 import java.time.format.DateTimeFormatter;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
@@ -88,8 +89,21 @@ private Msg(
         this.id = id;
         this.name = name;
         this.role = role;
-        this.content = Objects.nonNull(content) ? List.copyOf(content) : List.of();
-        this.metadata = Objects.nonNull(metadata) ? Map.copyOf(metadata) : Map.of();
+        this.content =
+                Objects.nonNull(content)
+                        ? content.stream().filter(Objects::nonNull).toList()
+                        : List.of();
+        this.metadata = new HashMap<>();
+        if (Objects.nonNull(metadata)) {
+            for (Map.Entry<String, Object> entry : metadata.entrySet()) {
+                String key = entry.getKey();
+                Object value = entry.getValue();
+                if (Objects.isNull(key) || Objects.isNull(value)) {
+                    continue;
+                }
+                this.metadata.put(key, value);
+            }
+        }
         this.timestamp = timestamp;
     }
 

agentscope-core/src/test/java/io/agentscope/core/msg/MsgTests.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2024-2025 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.msg;
+
+import io.agentscope.core.message.ContentBlock;
+import io.agentscope.core.message.Msg;
+import io.agentscope.core.message.MsgRole;
+import java.util.Map;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class MsgTests {
+
+    @Test
+    void testConstructor() {
+        Msg msg1 =
+                Msg.builder()
+                        .name("test")
+                        .role(MsgRole.SYSTEM)
+                        .content(new ContentBlock())
+                        .timestamp(String.valueOf(System.currentTimeMillis()))
+                        .metadata(Map.of("key", "value"))
+                        .build();
+        Assertions.assertNotNull(msg1);
+
+        Msg msg2 =
+                Msg.builder()
+                        .name("test")
+                        .role(MsgRole.SYSTEM)
+                        .timestamp(String.valueOf(System.currentTimeMillis()))
+                        .build();
+        Assertions.assertNotNull(msg2);
+    }
+}