@property<EOL><INDENT>def fill_value(self):<DEDENT>
return self._fill_value<EOL>
The fill value of the array.

Converting the SparseArray to a dense ndarray will fill the
array with this value.

.. warning::

   It's possible to end up with a SparseArray that has ``fill_value``
   values in ``sp_values``. This can occur, for example, when setting
   ``SparseArray.fill_value`` directly.