Django. Admin Tabular Inline initial data

admin.py

from django.utils.functional import curry

class DetailsInline(admin.TabularInline):
    model = Details
    # formset = DetailsFormset
    extra = 3

    def get_formset(self, request, obj=None, **kwargs):
        initial = []
        if request.method == "GET":
            initial.append({
                'label': 'first name',
            })
        formset = super(DetailsInline, self).get_formset(request, obj, **kwargs)
        formset.__init__ = curry(formset.__init__, initial=initial)
        return formset

models.py

class Employee(models.Model):
    username = models.CharField(_('Username'), max_length=150, null=False, blank=False)
    email = models.CharField(_('Email'), max_length=150, null=False, blank=False)

class Details(models.Model):
    employee = models.ForeignKey(Employee, verbose_name=_('Employee'), blank=False, null=False)
    label = models.CharField(_('Label'), max_length=150, null=False, blank=False)
    value = models.CharField(_('Value'), max_length=150, null=False, blank=False)

Thank you @LowerDeez & @serguitus, I ended up with replacing line 10 with if request.method == "GET" and (not obj or not obj.id): and it worked like a charm :)

PS - Also, didn't require to mention formset (line 5) explicitly in my case (since all custom changes needed were just the addition of initial data)