class_docstr: This class replaces all the missing values with the same dummy value given
  in advance.
class_docstr_tok: ["This","class","replaces","all","the","missing","values","with","the","same","dummy","value","given","in","advance","."]
code: def __call__(self, values: np.ndarray) -> np.ndarray:
      nan_indices = np.where(np.isnan(values))
      values[nan_indices] = self.dummy_value
      return values
  
imports: from typing import List, Optional, Union, Type
  import numpy
  import pandas
  from gluonts.core.component import validated
  from gluonts.dataset.common import DataEntry
  from gluonts.dataset.field_names import FieldName
  from gluonts.time_feature import TimeFeature
  from ._base import MapTransformation, SimpleTransformation
label_desc: Use image node_id 2 for calling the DummyValueImputation obj's underlying member method code with example usage: obj.__call__(values) and returns: values