Timestamp = pd.Timestamp
nan = np.nan
NaT = pd.NaT
df1 = pd.DataFrame({'col1': list('ac'), 'col2': ['b', nan], 'date': (
    Timestamp('2014-08-14'), NaT)})
df1['col2'] = df1['col2'].fillna('')
df1['date'] = [(d.strftime('%Y-%m-%d') if not pd.isnull(d) else '') for d in
    df1['date']]
print(df1)
Удалить dtype datetime NaT