Mapping statisticalCodeIds fails when there are multiple subfields you want to extract codes from

```
998": [
{
"target": "statisticalCodeIds.items",
"subfield": [
"c",
"h"
],
"description": "Statistical codes"
}
]

```
Exception
> File "/home/ssm-user/.local/share/virtualenvs/migration_ecok-UbKGs0an/lib/python3.9/site-packages/folio_migration_tools/marc_rules_transformation/rules_mapper_base.py", line 112, in handle_normal_mapping
> self.add_value_to_target(folio_record, target, [value])
> File "/home/ssm-user/.local/share/virtualenvs/migration_ecok-UbKGs0an/lib/python3.9/site-packages/folio_migration_tools/marc_rules_transformation/rules_mapper_base.py", line 253, in add_value_to_target
> elif schema_parent and target in rec[parent][-1]:
> IndexError: list index out of range
> Stack (most recent call last):
> File "/home/ssm-user/.pyenv/versions/3.9.9/lib/python3.9/runpy.py", line 197, in _run_module_as_main
> return _run_code(code, main_globals, None,
> File "/home/ssm-user/.pyenv/versions/3.9.9/lib/python3.9/runpy.py", line 87, in _run_code
> exec(code, run_globals)
> File "/home/ssm-user/.local/share/virtualenvs/migration_ecok-UbKGs0an/lib/python3.9/site-packages/folio_migration_tools/__main__.py", line 119, in
> main()
> File "/home/ssm-user/.local/share/virtualenvs/migration_ecok-UbKGs0an/lib/python3.9/site-packages/folio_migration_tools/__main__.py", line 69, in main
> task_obj.do_work()
> File "/home/ssm-user/.local/share/virtualenvs/migration_ecok-UbKGs0an/lib/python3.9/site-packages/folio_migration_tools/migration_tasks/bibs_transformer.py", line 99, in do_work
> logging.exception(file_obj, stack_info=True)
> 2022-05-25 21:26:26,554 CRITICAL File bibs_unsuppressed.mrc failed for unknown reason. Halting bibs_transformer.py:100