schema = dj.schema('test_tables')
@schema
class Test(dj.Manual):
    definition = """
    pk: int
    ----
    date=null: date
    """

Test.insert1((2, '2019-09-25'))
dj.Table._update(Test, 'date', None)

---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-33-b3f6114b7496> in <module>
----> 1 dj.Table._update(test.Test & 'pk=1', 'date', None)

AttributeError: module 'test' has no attribute 'Test'

In [34]: dj.Table._update(Test & 'pk=1', 'date', None)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-34-39bb5cd3e2c5> in <module>
----> 1 dj.Table._update(Test & 'pk=1', 'date', None)

~/anaconda3/lib/python3.7/site-packages/datajoint/table.py in _update(self, attrname, value)
    595             placeholder=placeholder,
    596             where_clause=self.where_clause)
--> 597         self.connection.query(command, args=(value, ) if value is not None else ())
    598
    599

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in query(self, query, args, as_dict, suppress_warnings, reconnect)
    206         cursor = self._conn.cursor(cursor=cursor_class)
    207         try:
--> 208             self.__execute_query(cursor, query, args, cursor_class, suppress_warnings)
    209         except errors.LostConnectionError:
    210             if not reconnect:

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in __execute_query(cursor, query, args, cursor_class, suppress_warnings)
    186                     # suppress all warnings arising from underlying SQL library
    187                     warnings.simplefilter("ignore")
--> 188                 cursor.execute(query, args)
    189         except client_errors as err:
    190             raise translate_query_error(err, query)

~/anaconda3/lib/python3.7/site-packages/pymysql/cursors.py in execute(self, query, args)
    166             pass
    167
--> 168         query = self.mogrify(query, args)
    169
    170         result = self._query(query)

~/anaconda3/lib/python3.7/site-packages/pymysql/cursors.py in mogrify(self, query, args)
    145
    146         if args is not None:
--> 147             query = query % self._escape_args(args, conn)
    148
    149         return query

TypeError: not enough arguments for format string

---------------------------------------------------------------------------
InternalError                             Traceback (most recent call last)
<ipython-input-36-3407a586c925> in <module>
----> 1 dj.Table._update(Test & 'pk=1', 'date', '')

~/anaconda3/lib/python3.7/site-packages/datajoint/table.py in _update(self, attrname, value)
    595             placeholder=placeholder,
    596             where_clause=self.where_clause)
--> 597         self.connection.query(command, args=(value, ) if value is not None else ())
    598
    599

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in query(self, query, args, as_dict, suppress_warnings, reconnect)
    206         cursor = self._conn.cursor(cursor=cursor_class)
    207         try:
--> 208             self.__execute_query(cursor, query, args, cursor_class, suppress_warnings)
    209         except errors.LostConnectionError:
    210             if not reconnect:

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in __execute_query(cursor, query, args, cursor_class, suppress_warnings)
    188                 cursor.execute(query, args)
    189         except client_errors as err:
--> 190             raise translate_query_error(err, query)
    191
    192     def query(self, query, args=(), *, as_dict=False, suppress_warnings=True, reconnect=None):

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in translate_query_error(client_error, query)
     48     if isinstance(client_error, client.err.InternalError) and client_error.args[0] == 1364:
     49         return errors.MissingAttributeError(*client_error.args[1:])
---> 50     raise client_error
     51
     52

~/anaconda3/lib/python3.7/site-packages/datajoint/connection.py in __execute_query(cursor, query, args, cursor_class, suppress_warnings)
    186                     # suppress all warnings arising from underlying SQL library
    187                     warnings.simplefilter("ignore")
--> 188                 cursor.execute(query, args)
    189         except client_errors as err:
    190             raise translate_query_error(err, query)

~/anaconda3/lib/python3.7/site-packages/pymysql/cursors.py in execute(self, query, args)
    168         query = self.mogrify(query, args)
    169
--> 170         result = self._query(query)
    171         self._executed = query
    172         return result

~/anaconda3/lib/python3.7/site-packages/pymysql/cursors.py in _query(self, q)
    326         self._last_executed = q
    327         self._clear_result()
--> 328         conn.query(q)
    329         self._do_get_result()
    330         return self.rowcount

~/anaconda3/lib/python3.7/site-packages/pymysql/connections.py in query(self, sql, unbuffered)
    515                 sql = sql.encode(self.encoding, 'surrogateescape')
    516         self._execute_command(COMMAND.COM_QUERY, sql)
--> 517         self._affected_rows = self._read_query_result(unbuffered=unbuffered)
    518         return self._affected_rows
    519

~/anaconda3/lib/python3.7/site-packages/pymysql/connections.py in _read_query_result(self, unbuffered)
    730         else:
    731             result = MySQLResult(self)
--> 732             result.read()
    733         self._result = result
    734         if result.server_status is not None:

~/anaconda3/lib/python3.7/site-packages/pymysql/connections.py in read(self)
   1073     def read(self):
   1074         try:
-> 1075             first_packet = self.connection._read_packet()
   1076
   1077             if first_packet.is_ok_packet():

~/anaconda3/lib/python3.7/site-packages/pymysql/connections.py in _read_packet(self, packet_type)
    682
    683         packet = packet_type(buff, self.encoding)
--> 684         packet.check_error()
    685         return packet
    686

~/anaconda3/lib/python3.7/site-packages/pymysql/protocol.py in check_error(self)
    218             errno = self.read_uint16()
    219             if DEBUG: print("errno =", errno)
--> 220             err.raise_mysql_exception(self._data)
    221
    222     def dump(self):

~/anaconda3/lib/python3.7/site-packages/pymysql/err.py in raise_mysql_exception(data)
    107         errval = data[3:].decode('utf-8', 'replace')
    108     errorclass = error_map.get(errno, InternalError)
--> 109     raise errorclass(errno, errval)

InternalError: (1292, "Incorrect date value: '' for column `test_tables`.`test`.`date` at row 1")