class_docstr: A `Predictor` that always produces the same value as forecast.
  
  Parameters
  ----------
  value
      The value to use as forecast.
  prediction_length
      Prediction horizon.
code: def predict_item(self, item: DataEntry) -> SampleForecast:
      samples_shape = self.num_samples, self.prediction_length
      samples = np.full(samples_shape, self.value)
      return SampleForecast(
          samples=samples,
          start_date=forecast_start(item),
          item_id=item.get("item_id"),
      )
  
file_path: gluonts/src/gluonts/model/trivial/constant.py
imports: import numpy
  from gluonts.core.component import validated
  from gluonts.dataset.common import DataEntry
  from gluonts.dataset.field_names import FieldName
  from gluonts.dataset.util import forecast_start
  from gluonts.model.forecast import SampleForecast
  from gluonts.model.predictor import RepresentablePredictor
label_desc: Use image node_id 2 for calling the ConstantValuePredictor obj's underlying member method code with example usage: obj.predict_item(item) and returns: SampleForecast