mistake in upgrade script

You might want to take a look at the following snippet:
private function create_phone_number_digits_column( $oldversion ) {
$this->columns->create(
AWPCP_TABLE_ADS,
‘phone_number_digits’,
$this->database_helper->replace_charset_and_collate(
“VARCHAR(25) CHARACTER SET <charset> COLLATE <collate> NOT NULL DEFAULT ” AFTER ad_contact_phone”
)
);
}

It fails because you can’t have not null default null. There probably should be a blank between the two single quotes.