django表单添加返回“ NoneType”对象的项目不是可调用错误

def add_player( request, team_season_id ):
    team_season = get_object_or_404( TeamSeasonConference, pk=team_season_id )

    player_form = PlayerForm()
    return render_to_response( \'backoffice/organization/add_player.html\', {
        \'player_form\': player_form,
        \'team_season\': team_season,
        \'player\': None
    }, context_instance=RequestContext( request ) )

Traceback:
File \"/usr/lib/pymodules/python2.6/django/core/handlers/base.py\" in get_response
  92.                 response = callback(request, *callback_args, **callback_kwargs)
File \"/mypath/apps/account/decorators.py\" in __call__
  73.             return self.view_func(request, *args, **kwargs)
File \"/mypath/apps/backoffice/views.py\" in add_player
  877.     player_form = PlayerForm()
File \"/usr/lib/pymodules/python2.6/django/forms/models.py\" in __init__
  218.             self.instance = opts.model()

Exception Type: TypeError at /backoffice/roster/add/player/2/
Exception Value: \'NoneType\' object is not callable

class PlayerForm( forms.ModelForm ):
    CLASS_CHOICES = (
        (\'\', \'-----\'),
    (\'FR\', \'freshman\'),
    (\'RS-FR\', \'red-shirt freshman\'),
    (\'SO\', \'sophomore\'),
    (\'RS-SO\', \'red-shirt sophomore\'),
    (\'JR\', \'junior\'),
    (\'RS-JR\', \'red-shirt junior\'),
    (\'SR\', \'senior\'),
    (\'RS-SR\', \'red-shirt senior\'),
)

first_name = forms.CharField( max_length=100, required=False, label=\"First\" )
last_name = forms.CharField( max_length=100, label=\"Last\" )

jersey = forms.IntegerField( min_value=0, required=False, label=\"Jersey\" )
height = forms.CharField( max_length=10, required=False )
weight = forms.IntegerField( required=False, min_value=0 )
age = forms.IntegerField( required=False, min_value=0 )
year = forms.TypedChoiceField( choices=CLASS_CHOICES, required=False, empty_value=\'\' )
varsity_letters = forms.IntegerField( required=False, min_value=0 )
position = forms.CharField( max_length=20, required=False )
hometown = forms.CharField( required=False )
major = forms.CharField( max_length=100, required=False )
freeform_school = forms.CharField( required=False, label=\"HS\" )
description = forms.CharField (widget=forms.Textarea, required=False )
HSSN = forms.CharField( max_length=8, required=False )
mugshot = forms.FileField( widget=forms.FileInput(), required=False )
team_season_connection = forms.ModelMultipleChoiceField(queryset=TeamSeasonConference.objects.filter(team = 1), required=False, widget=forms.SelectMultiple)

    def save(self, commit=True, request=None, user=None):
        player = super( PlayerForm, self ).save( commit=False )

        if commit:
            # save the player
            player.save()
            return player

class Player( models.Model ):

CLASS_CHOICES = (
    (\'FR\', \'freshman\'),
    (\'RS-FR\', \'red-shirt freshman\'),
    (\'SO\', \'sophomore\'),
    (\'RS-SO\', \'red-shirt sophomore\'),
    (\'JR\', \'junior\'),
    (\'RS-JR\', \'red-shirt junior\'),
    (\'SR\', \'senior\'),
    (\'RS-SR\', \'red-shirt senior\'),
)

first_name = models.CharField( max_length=100 )
last_name = models.CharField( max_length=100 )
suffix = models.CharField( max_length=5, blank=True )
nickname = models.CharField( max_length=100, blank=True )
slug = models.SlugField( max_length=200, blank=True, help_text=\"Used for associating content. (lowercase, hyphens sted spaces, no punctuation)\" )

team_season_connection = models.ManyToManyField( TeamSeasonConference, related_name=\'career_roster\', blank=True)
team_season = models.ForeignKey( TeamSeasonConference, related_name=\'roster\', blank=True )
height = models.CharField( max_length=10, blank=True )
weight = models.PositiveIntegerField( blank=True, null=True )
age = models.PositiveIntegerField( blank=True, null=True )
year = models.CharField( max_length=5, choices=CLASS_CHOICES, blank=True, db_index=True )
varsity_letters = models.PositiveIntegerField( blank=True, null=True )
position = models.CharField( max_length=20, blank=True )
jersey = models.PositiveIntegerField( blank=True, null=True )
mugshot = models.ForeignKey( \'content.Photo\', null=True, blank=True )
profile = models.ForeignKey( \'content.Story\', null=True, blank=True, help_text=\"Optionally link player to a profile story.\")

major = models.CharField( max_length=100, blank=True)

freeform_school = models.CharField( max_length=100, blank=True, help_text=\"Take care to enter the school consistantly across players.\" )
hometown = models.CharField( max_length=100, blank=True, help_text=\"Town and state, i.e. Orlando, FL.\" )
offered_scholarship = models.BooleanField( help_text=\"Check if user has a scholarship offer.\" )
description = models.TextField( blank=True )

antagonist = models.BooleanField( help_text=\"To be used as indicator of whether this player is the season\'s antagonist\" )
pluck_user = models.ForeignKey ( \'auth.User\', null=True, blank=True, help_text=\"Optionally link to user login\")

# reverse generic relations
scrapbooks = generic.GenericRelation( Scrapbook )