from typing import Mapping
from typing import Optional
from typing import List


def _process_tags(tags: Mapping[str, str]) -> Optional[str]:
    """Outputs snapshot tags as a multi-line string."""
    if not tags:
        return None

    output: List[str] = ['Tags:']
    for key, value in tags.items():
        output.append(f'  {key}: {value}')

    return '\n'.join(output)