geopandas series fillna results in float

Question

As seen below, why does fillna results in a float number instead of a Point?

In [4]: import numpy as np                                                                                                                                                                                                                     

In [5]: import geopandas as gpd                                                                                                                                                                                                                

In [8]: import shapely                                                                                                                                                                                                                         

In [9]: df_tmp = gpd.GeoDataFrame([['a', np.NaN], ['b', shapely.geometry.Point(35, 70)]], columns=['id', 'geometry'])                                                                                                                          

In [10]: df_tmp                                                                                                                                                                                                                                
Out[10]: 
  id       geometry
0  a            NaN
1  b  POINT (35 70)

In [11]: df_tmp.geometry.fillna(shapely.geometry.Point(90, 0))                                                                                                                                                                                 
Out[11]: 
0               90
1    POINT (35 70)
Name: geometry, dtype: object

version info:

In [12]: gpd.__version__                                                                                                                                                                                                                       
Out[12]: '0.5.0'

In [13]: shapely.__version__                                                                                                                                                                                                                   
Out[13]: '1.6.4.post2'

In [14]: np.__version__                                                                                                                                                                                                                        
Out[14]: '1.16.4'

Answer 1

Check the documentation for fillna in pandas.

https://pandas.pydata.org/pandas-docs/stable/reference/api/pandas.DataFrame.fillna.html

A shapely geometry may not be a valid argument for that function.