class_docstr: Replaces missing values in a numpy array (NaNs) with a dummy value and adds
  an "observed"-indicator that is ``1`` when values are observed and ``0``
  when values are missing.
  
  Parameters
  ----------
  target_field
      Field for which missing values will be replaced
  output_field
      Field name to use for the indicator
  imputation_method
      One of the methods from ImputationStrategy. If set to None, no
      imputation is done and only the indicator is included.
class_docstr_tok: ["Replaces","missing","values","in","a","numpy","array","(","NaNs",")","with","a","dummy","value","and","adds","an","``","observed","''","-indicator","that","is","``","1","``","when","values","are","observed","and","``","0","``","when","values","are","missing",".","Parameters","--","--","--","--","--","target_field","Field","for","which","missing","values","will","be","replaced","output_field","Field","name","to","use","for","the","indicator","imputation_method","One","of","the","methods","from","ImputationStrategy",".","If","set","to","None",",","no","imputation","is","done","and","only","the","indicator","is","included","."]
code: def __init__(
      self,
      target_field: str,
      output_field: str,
      imputation_method: Optional[
          MissingValueImputation
      ] = DummyValueImputation(0.0),
      dtype: Type = np.float32,
  ) -> None:
      self.target_field = target_field
      self.output_field = output_field
      self.dtype = dtype
      self.imputation_method = imputation_method
  
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 1 to create a new AddObservedValuesIndicator object from inherited base classes: SimpleTransformation with example: obj = AddObservedValuesIndicator(target_field, output_field, imputation_method, dtype)