Fix creation of DataFactory pipeline (#19836)

* Fix creation of DataFactory pipeline

The error is:
```
java.lang.IllegalArgumentException: Body parameter value must not be null. (parameter #10)
    for method PipelinesService.createRun
	at retrofit2.Utils.methodError(Utils.java:52)
	at retrofit2.Utils.methodError(Utils.java:42)
	at retrofit2.Utils.parameterError(Utils.java:61)
	at retrofit2.ParameterHandler$Body.apply(ParameterHandler.java:408)
	at retrofit2.RequestFactory.create(RequestFactory.java:117)
	at retrofit2.OkHttpCall.createRawCall(OkHttpCall.java:192)
	at retrofit2.OkHttpCall.execute(OkHttpCall.java:175)
	at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:40)
	at retrofit2.adapter.rxjava.CallExecuteOnSubscribe.call(CallExecuteOnSubscribe.java:24)
	at rx.Observable.unsafeSubscribe(Observable.java:10327)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33)
	at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:48)
	at rx.internal.operators.OnSubscribeLift.call(OnSubscribeLift.java:30)
	at rx.Observable.unsafeSubscribe(Observable.java:10327)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33)
	at rx.Observable.unsafeSubscribe(Observable.java:10327)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:48)
	at rx.internal.operators.OnSubscribeMap.call(OnSubscribeMap.java:33)
	at rx.Observable.subscribe(Observable.java:10423)
	at rx.Observable.subscribe(Observable.java:10390)
	at rx.observables.BlockingObservable.forEach(BlockingObservable.java:111)
```

The parameter #10 is `parameters` which represent request body

* Fix typo

sdk/datafactory/mgmt-v2018_06_01/src/main/java/com/microsoft/azure/management/datafactory/v2018_06_01/implementation/PipelinesInner.java

@@ -20,6 +20,7 @@
 import com.microsoft.rest.ServiceResponse;
 import com.microsoft.rest.Validator;
 import java.io.IOException;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import okhttp3.ResponseBody;
@@ -766,7 +767,7 @@ public Observable<ServiceResponse<CreateRunResponseInner>> createRunWithServiceR
         final Boolean isRecovery = null;
         final String startActivityName = null;
         final Boolean startFromFailure = null;
-        final Map<String, Object> parameters = null;
+        final Map<String, Object> parameters = new HashMap<>();
         return service.createRun(this.client.subscriptionId(), resourceGroupName, factoryName, pipelineName, this.client.apiVersion(), referencePipelineRunId, isRecovery, startActivityName, startFromFailure, parameters, this.client.acceptLanguage(), this.client.userAgent())
             .flatMap(new Func1<Response<ResponseBody>, Observable<ServiceResponse<CreateRunResponseInner>>>() {
                 @Override