fix telnet invoke NPE #2218 (#2273)

* fix issue #2218
* add some unit tests

dubbo-rpc/dubbo-rpc-dubbo/src/main/java/com/alibaba/dubbo/rpc/protocol/dubbo/telnet/InvokeTelnetHandler.java

@@ -60,6 +60,19 @@ private static boolean isMatch(Class<?>[] types, List<Object> args) {
         for (int i = 0; i < types.length; i++) {
             Class<?> type = types[i];
             Object arg = args.get(i);
+
+            if (arg == null) {
+                // if the type is primitive, the method to invoke will cause NullPointerException definitely
+                // so we can offer a specified error message to the invoker in advance and avoid unnecessary invoking
+                if (type.isPrimitive()) {
+                    throw new NullPointerException(String.format(
+                            "The type of No.%d parameter is primitive(%s), but the value passed is null.", i + 1, type.getName()));
+                }
+
+                // if the type is not primitive, we choose to believe what the invoker want is a null value
+                continue;
+            }
+
             if (ReflectUtils.isPrimitive(arg.getClass())) {
                 if (!ReflectUtils.isPrimitive(type)) {
                     return false;

dubbo-rpc/dubbo-rpc-dubbo/src/test/java/com/alibaba/dubbo/rpc/protocol/dubbo/support/DemoService.java

@@ -57,4 +57,6 @@ public interface DemoService {
 
     NonSerialized returnNonSerialized();
 
+    long add(int a, long b);
+
 }

dubbo-rpc/dubbo-rpc-dubbo/src/test/java/com/alibaba/dubbo/rpc/protocol/dubbo/support/DemoServiceImpl.java

@@ -103,4 +103,9 @@ public void nonSerializedParameter(NonSerialized ns) {
     public NonSerialized returnNonSerialized() {
         return new NonSerialized();
     }
+
+    public long add(int a, long b) {
+        return a + b;
+    }
+
 }

dubbo-rpc/dubbo-rpc-dubbo/src/test/java/com/alibaba/dubbo/rpc/protocol/dubbo/telnet/InvokerTelnetHandlerTest.java

@@ -33,6 +33,7 @@
 
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.fail;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.BDDMockito.given;
 import static org.mockito.Mockito.mock;
@@ -68,6 +69,41 @@ public void testInvokeDefaultSService() throws RemotingException {
         assertTrue(result.contains("Use default service com.alibaba.dubbo.rpc.protocol.dubbo.support.DemoService.\r\n\"ok\"\r\n"));
     }
 
+    @SuppressWarnings("unchecked")
+    @Test
+    public void testInvokeByPassingNullValue() throws RemotingException {
+        mockInvoker = mock(Invoker.class);
+        given(mockInvoker.getInterface()).willReturn(DemoService.class);
+        given(mockInvoker.getUrl()).willReturn(URL.valueOf("dubbo://127.0.0.1:20883/demo"));
+        given(mockInvoker.invoke(any(Invocation.class))).willReturn(new RpcResult("ok"));
+        mockChannel = mock(Channel.class);
+        given(mockChannel.getAttribute("telnet.service")).willReturn("org.apache.dubbo.rpc.protocol.dubbo.support.DemoService");
+        given(mockChannel.getLocalAddress()).willReturn(NetUtils.toAddress("127.0.0.1:5555"));
+        given(mockChannel.getRemoteAddress()).willReturn(NetUtils.toAddress("127.0.0.1:20883"));
+        DubboProtocol.getDubboProtocol().export(mockInvoker);
+        // pass null value to parameter of primitive type
+        try {
+            invoke.telnet(mockChannel, "DemoService.add(null, 2)");
+            fail("It should cause a NullPointerException by the above code.");
+        } catch (NullPointerException ex) {
+            String message = ex.getMessage();
+            assertEquals("The type of No.1 parameter is primitive(int), but the value passed is null.", message);
+        }
+        try {
+            invoke.telnet(mockChannel, "DemoService.add(1, null)");
+            fail("It should cause a NullPointerException by the above code.");
+        } catch (NullPointerException ex) {
+            String message = ex.getMessage();
+            assertEquals("The type of No.2 parameter is primitive(long), but the value passed is null.", message);
+        }
+        // pass null value to parameter of object type
+        try {
+            invoke.telnet(mockChannel, "DemoService.sayHello(null)");
+        } catch (NullPointerException ex) {
+            fail("It shouldn't cause a NullPointerException by the above code.");
+        }
+    }
+
     @SuppressWarnings("unchecked")
     @Test
     public void testInvokeAutoFindMethod() throws RemotingException {