if not self.caller.db.has('mark'):
            self.caller.db.mark = {}

"RETURNS ERROR"
"""
Traceback (most recent call last):
  File "d:\muddev\evennia\evennia\commands\cmdhandler.py", line 591, in _run_command
    ret = cmd.func()
  File "d:\muddev\mygame\commands\command.py", line 330, in func
    if not self.caller.db.has('mark'):
TypeError: 'NoneType' object is not callable
"""


"Working Alternative"
class CmdMark(Command):
    """
    Mark the current location.

    Usage:
        mark <custom mark name>

    Marks the player's current location, using the provided arguments.
    For a list of marks, simply type 'mark' with no argument.
    """
    key = "mark"

    def func(self):
        if not self.caller.db.mark:
            self.caller.db.mark = {}
        if not self.args:
            marks = self.caller.db.mark
            return self.caller.msg(f"{marks}")

        self.caller.db.mark[self.args] = self.caller.location.dbref
        self.caller.msg(f"{self.args} was added to your list of marks as {self.caller.location}.")