code: def _set_default_fill_value(encoding, dataset):
      """Set default fill values.
  
      Avoid _FillValue attribute being added to coordinate variables
      (https://github.com/pydata/xarray/issues/1865).
      """
      coord_vars = []
      for data_array in dataset.values():
          coord_vars.extend(
              set(data_array.dims).intersection(data_array.coords)
          )
      for coord_var in coord_vars:
          encoding.setdefault(coord_var, {})
          encoding[coord_var].update({"_FillValue": None})
      return encoding
  
file_path: satpy/satpy/cf/encoding.py
imports: import logging
  import numpy
  import xarray
  from xarray.coding.times import CFDatetimeCoder
label_desc: Use image node_id 2 for calling a global function with example usage: _set_default_fill_value(encoding, dataset) and returns: encoding