@Override
      public boolean hasNext() {
        if (exhausted) {
          return false;
        }

        if (nextSplit != null) {
          return true;
        }

        final InputSplit split;
        try {
          split = provider.getNextInputSplit(getRuntimeContext().getUserCodeClassLoader());
        } catch (InputSplitProviderException e) {
          throw new RuntimeException("Could not retrieve next input split.", e);
        }

        if (split != null) {
          this.nextSplit = split;
          return true;
        } else {
          exhausted = true;
          return false;
        }
      }
Returns the {@code InputFormat}. This is only needed because we need to set the input split
assigner on the {@code StreamGraph}.
amoro-format-mixed/amoro-mixed-flink/amoro-mixed-flink-common/src/main/java/org/apache/amoro/flink/table/UnkeyedInputFormatSourceFunction.java