Flink 1.11 SQL error: No operators defined in streaming topology. Cannot execute.

[Lu Weizheng]

Hi,

I am using Flink 1.11 SQL using java. All my operations are in SQL. I create 
source tables and insert result into sink tables. No other Java operators. I 
execute it in Intellij. I can get the final result in the sink tables. However 
I get the following error. I am not sure it is a bug or there is something 
wrong in my code? Acutally it does not affect the computation.

Exception in thread "main" java.lang.IllegalStateException: No operators 
defined in streaming topology. Cannot execute.
at 
org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.getStreamGraphGenerator(StreamExecutionEnvironment.java:1872)
at 
org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.getStreamGraph(StreamExecutionEnvironment.java:1863)
at 
org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.getStreamGraph(StreamExecutionEnvironment.java:1848)
at 
org.apache.flink.streaming.api.environment.StreamExecutionEnvironment.execute(StreamExecutionEnvironment.java:1699)
at com.flink.tutorials.java.projects.iot.IoTSQLDemo.main()

Here's my code:

        EnvironmentSettings fsSettings =   
EnvironmentSettings.newInstance().useBlinkPlanner().inStreamingMode().build();
        StreamExecutionEnvironment env = 
StreamExecutionEnvironment.getExecutionEnvironment();
        StreamTableEnvironment tEnv = StreamTableEnvironment.create(env, 
fsSettings);

        // create source and sink tables...

        tEnv.executeSql("INSERT INTO sensor_1min_avg " +
                "SELECT " +
                "  room, " +
                "  AVG(temp) AS avg_temp," +
                "  TUMBLE_END(ts, INTERVAL '1' MINUTE) AS end_ts " +
                "FROM sensor " +
                "GROUP BY room, TUMBLE(ts, INTERVAL '1' MINUTE)");

        env.execute("table api");