недопустимый литерал для int () с основанием 10: '' в Django на Postgres, но не в SQLite

Question

Я запускаю приложение Django в течение нескольких лет, и оно неожиданно начало выдавать ошибки при обновлении базы данных Postgres, используемой для управления живым сайтом. Когда я тестирую с использованием базы данных SQLite, никаких проблем не возникает. Всякий раз, когда я пытаюсь внести какие-либо изменения в объекты базы данных, я получаю ошибку invalid literal for int() with base 10: ''.

Это трассировка, которую я получаю:

Traceback:

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\core\handlers\exception.py" in inner
  41.             response = get_response(request)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\core\handlers\base.py" in _get_response
  187.                 response = self.process_exception_by_middleware(e, request)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\core\handlers\base.py" in _get_response
  185.                 response = wrapped_callback(request, *callback_args, **callback_kwargs)

File ".\Indicators\views.py" in edit_indicator
  227.             indicator_to_be_edited.save()

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\base.py" in save
  806.                        force_update=force_update, update_fields=update_fields)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\base.py" in save_base
  836.             updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\base.py" in _save_table
  903.                                       forced_update)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\base.py" in _do_update
  953.         return filtered._update(values) > 0

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\query.py" in _update
  664.         return query.get_compiler(self.db).execute_sql(CURSOR)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\sql\compiler.py" in execute_sql
  1191.         cursor = super(SQLUpdateCompiler, self).execute_sql(result_type)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\sql\compiler.py" in execute_sql
  863.             sql, params = self.as_sql()

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\sql\compiler.py" in as_sql
  1157.                 val = field.get_db_prep_save(val, connection=self.connection)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\fields\__init__.py" in get_db_prep_save
  770.                                       prepared=False)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\fields\__init__.py" in get_db_prep_value
  762.             value = self.get_prep_value(value)

File "C:\ProgramData\Anaconda34\envs\py34\lib\site-packages\django\db\models\fields\__init__.py" in get_prep_value
  1853.         return int(value)

Exception Type: ValueError at /edit-indicator/
Exception Value: invalid literal for int() with base 10: ''

Это модель, которую я пытаюсь обновить:

class Indicator(models.Model):
    time_periods = get_time_periods()

    months = get_months()

    calculations = get_calculations()

    sex_ids = get_all_sexes()

    age_ids = sort_all_ages()

    operands = (
       ('+', '+'),
       ('-', '-'),
       ('*', '*'),
       ('/', '/')
    )

    salt_options = get_salt_options_as_tuple()

    qof_data_choices = get_qof_choices_as_tuple()

    id = models.IntegerField(unique=True, primary_key=True)
    source_data_family = models.ForeignKey(IndicatorFamily, on_delete=models.CASCADE, blank=True)
    qof_source_data = models.CharField(max_length=100, choices=qof_data_choices, blank=True)
    source_sheet = models.CharField(max_length=200, blank=True)
    year_range = models.CharField(max_length=2, blank=True)
    time_period = models.CharField(max_length=30, choices=time_periods, blank=True)
    ageId = models.IntegerField(choices=age_ids, blank=True)
    sexId = models.IntegerField(choices=sex_ids)
    calculation = models.CharField(max_length=30, choices=calculations, blank=True)
    rate = models.IntegerField(blank=True, null=True)
    value_declared_independently = models.BooleanField(default=False)
    value_column_name = models.CharField(max_length=200, blank=True)
    numerator_starts_with_financial_year = models.BooleanField(default=False)
    numerator = models.CharField(max_length=200, blank=True)
    salt_numerator = models.CharField(max_length=200, blank=True, choices=salt_options)
    salt_numerator_operand = models.CharField(max_length=2, choices=operands, blank=True)
    salt_numerator_2 = models.CharField(max_length=200, blank=True, choices=salt_options)
    numerator_minus_not_caseness = models.BooleanField(default=False)
    iapt_q_m_variable_type = models.CharField(max_length=200, blank=True)
    iapt_q_m_variable_a = models.CharField(max_length=200, blank=True)
    iapt_q_m_variable_b = models.CharField(max_length=200, blank=True)
    iapt_q_m_variable_type_denominator = models.CharField(max_length=200, blank=True)
    iapt_q_m_variable_a_denominator = models.CharField(max_length=200, blank=True)
    iapt_q_m_variable_b_denominator = models.CharField(max_length=200, blank=True)
    denominator_starts_with_financial_year = models.BooleanField(default=False)
    denominator = models.CharField(max_length=200, blank=True)
    denominator_minus_not_caseness = models.BooleanField(default=False)
    denominator_source_sheet = models.CharField(max_length=200, blank=True)
    salt_denominator = models.CharField(max_length=200, blank=True, choices=salt_options)
    salt_denominator_operand = models.CharField(max_length=2, choices=operands, blank=True)
    salt_denominator_2 = models.CharField(max_length=200, blank=True, choices=salt_options)
    add_denominator_column = models.CharField(max_length=200, blank=True)
    additional_denominator_column_starts_with_financial_year = models.BooleanField(default=False)
    adjust_denominator_for_person_years = models.BooleanField(default=False)
    ccg_over_18_population_as_denominator = models.BooleanField(default=False)
    ccg_total_population_as_denominator = models.BooleanField(default=False)
    is_count = models.BooleanField(default=False)
    is_percentage = models.BooleanField(default=False)
    ccg_to_stp = models.BooleanField(default=False)
    gp_to_upper_tier_la = models.BooleanField(default=False)
    ccg_lookup_required = models.BooleanField(default=False)
    drop_depression = models.BooleanField(default=False)
    count_non_nulls = models.BooleanField(default=False)
    non_null_columns = models.CharField(max_length=300, blank=True)
    drop_eng_row = models.BooleanField(default=False)
    months_to_quarter = models.BooleanField(default=False)
    snapshot = models.BooleanField(default=False)
    asterisk_as_two = models.BooleanField(default=False)
    creator = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    denominator_2_equals_denominator = models.BooleanField(default=False)
    do_not_suppress_small_numbers = models.BooleanField(default=False)
    numerator_is_num_minus_denom = models.BooleanField(default=False)
    stp_is_average_not_sum = models.BooleanField(default=False)
    mental_health_trust_geographies = models.BooleanField(default=False)
    filter_by = models.CharField(max_length=200, blank=True)
    quarters_to_year = models.BooleanField(default=False)

Может кто-нибудь пролить свет на то, почемуэто будет происходить?