fix:单元测试时Packet模块中遇到的NullPointerException

add:KeyChain单元测试

src/main/java/packet/CPacket.java

@@ -157,12 +157,15 @@ public class CPacket implements InteractWithField, IEncodingAble {
 
             // 填充只读区
             // 首先清除所有的Block
-            minPacket.readOnlyField.clearBlocks();
-            block = new SelfEncodingBase().selfWireEncode(this.payload);
-            if (block == null) {
-                return false;
+            if (this.payload.getValue() != null){
+                minPacket.readOnlyField.clearBlocks();
+                block = new SelfEncodingBase().selfWireEncode(this.payload);
+                if (block == null) {
+                    return false;
+                }
+                minPacket.readOnlyField.addBlock(block);
             }
-            minPacket.readOnlyField.addBlock(block);
+
 
             // 填充标识区
             // 首先清除所有的标识