Fixed #12689: Fixed admin validation to report an error on invalid exclude...

        if len(flattened_fieldsets) > len(set(flattened_fieldsets)):

            raise ImproperlyConfigured('There are duplicate field(s) in %s.fieldsets' % cls.__name__)

    # exclude

    if cls.exclude: # default value is None

        check_isseq(cls, 'exclude', cls.exclude)

        for field in cls.exclude:

            check_formfield(cls, model, opts, 'exclude', field)

            try:

                f = opts.get_field(field)

            except models.FieldDoesNotExist:

                # If we can't find a field on the model that matches,

                # it could be an extra field on the form.

                continue

        if len(cls.exclude) > len(set(cls.exclude)):

            raise ImproperlyConfigured('There are duplicate field(s) in %s.exclude' % cls.__name__)

    # form

    if hasattr(cls, 'form') and not issubclass(cls.form, BaseModelForm):

    ...

ImproperlyConfigured: 'InvalidFields.fields' refers to field 'spam' that is missing from the form.

# Tests for basic validation of 'exclude' option values (#12689)

>>> class ExcludedFields1(admin.ModelAdmin):

...     exclude = ('foo')

>>> validate(ExcludedFields1, Book)

Traceback (most recent call last):

    ...

ImproperlyConfigured: 'ExcludedFields1.exclude' must be a list or tuple.

>>> class ExcludedFields2(admin.ModelAdmin):

...     exclude = ('name', 'name')

>>> validate(ExcludedFields2, Book)

Traceback (most recent call last):

    ...

ImproperlyConfigured: There are duplicate field(s) in ExcludedFields2.exclude

>>> class ExcludedFieldsInline(admin.TabularInline):

...     model = Song

...     exclude = ('foo')

>>> class ExcludedFieldsAlbumAdmin(admin.ModelAdmin):

...     model = Album

...     inlines = [ExcludedFieldsInline]

>>> validate(ExcludedFieldsAlbumAdmin, Album)

Traceback (most recent call last):

    ...

ImproperlyConfigured: 'ExcludedFieldsInline.exclude' must be a list or tuple.

# Regression test for #9932 - exclude in InlineModelAdmin

# should not contain the ForeignKey field used in ModelAdmin.model