stub: Add null check for responseObserver (#10083)

* stub:Add null check for responseObserver

Fixes #10064

stub/src/main/java/io/grpc/stub/ClientCalls.java

@@ -73,6 +73,7 @@ public final class ClientCalls {
    */
   public static <ReqT, RespT> void asyncUnaryCall(
       ClientCall<ReqT, RespT> call, ReqT req, StreamObserver<RespT> responseObserver) {
+    checkNotNull(responseObserver, "responseObserver");
     asyncUnaryRequestCall(call, req, responseObserver, false);
   }
 
@@ -86,6 +87,7 @@ public final class ClientCalls {
    */
   public static <ReqT, RespT> void asyncServerStreamingCall(
       ClientCall<ReqT, RespT> call, ReqT req, StreamObserver<RespT> responseObserver) {
+    checkNotNull(responseObserver, "responseObserver");
     asyncUnaryRequestCall(call, req, responseObserver, true);
   }
 
@@ -102,6 +104,7 @@ public final class ClientCalls {
   public static <ReqT, RespT> StreamObserver<ReqT> asyncClientStreamingCall(
       ClientCall<ReqT, RespT> call,
       StreamObserver<RespT> responseObserver) {
+    checkNotNull(responseObserver, "responseObserver");
     return asyncStreamingRequestCall(call, responseObserver, false);
   }
 
@@ -116,6 +119,7 @@ public final class ClientCalls {
    */
   public static <ReqT, RespT> StreamObserver<ReqT> asyncBidiStreamingCall(
       ClientCall<ReqT, RespT> call, StreamObserver<RespT> responseObserver) {
+    checkNotNull(responseObserver, "responseObserver");
     return asyncStreamingRequestCall(call, responseObserver, true);
   }
 

stub/src/test/java/io/grpc/stub/ClientCallsTest.java

@@ -503,6 +503,50 @@ public class ClientCallsTest {
     assertThat(requests).isEmpty();
   }
 
+  @Test
+  public void checkForNullInAsyncUnaryCall()  {
+    NoopClientCall<Integer, String> call = new NoopClientCall<>();
+    try {
+      ClientCalls.asyncUnaryCall(call, Integer.valueOf(1), null);
+      fail("Should have gotten an exception for the null responseObserver");
+    } catch (NullPointerException e) {
+      assertEquals("responseObserver", e.getMessage());
+    }
+  }
+
+  @Test
+  public void checkForNullInBidiCall()  {
+    NoopClientCall<Integer, String> call = new NoopClientCall<>();
+    try {
+      ClientCalls.asyncBidiStreamingCall(call, null);
+      fail("Should have gotten an exception for the null responseObserver");
+    } catch (NullPointerException e) {
+      assertEquals("responseObserver", e.getMessage());
+    }
+  }
+
+  @Test
+  public void checkForNullInClientStreamCall()  {
+    NoopClientCall<Integer, String> call = new NoopClientCall<>();
+    try {
+      ClientCalls.asyncClientStreamingCall(call, null);
+      fail("Should have gotten an exception for the null responseObserver");
+    } catch (NullPointerException e) {
+      assertEquals("responseObserver", e.getMessage());
+    }
+  }
+
+  @Test
+  public void checkForNullInServerStreamCall()  {
+    NoopClientCall<Integer, String> call = new NoopClientCall<>();
+    try {
+      ClientCalls.asyncServerStreamingCall(call, Integer.valueOf(1), null);
+      fail("Should have gotten an exception for the null responseObserver");
+    } catch (NullPointerException e) {
+      assertEquals("responseObserver", e.getMessage());
+    }
+  }
+
   @Test
   public void callStreamObserverPropagatesFlowControlRequestsToCall()
       throws Exception {