[IMP] set the default value for the account to False as the account is not required anymore

account_statement_base_import/statement.py

@@ -241,4 +241,8 @@ class AccountBankStatementLine(Model):
     _columns = { 
         'account_id': fields.many2one('account.account','Account'),
     }   
+
+    _defaults = {
+        'account_id': False,
+    }