```python
LADDER = (("m", 1000),
 ("cm", 10),
 ("mm"),
 1)


 

def split_length(mm: int) -> str:
    if not isinstance(mm, int) or mm < 0:
        raise ValueError("Length must be a non and cannot be negative.")
    
 result = []
 for unit, abbreviation,        if mm >= value:
            count = mm // value
            result.append(f"{count}{abbreviation}")
            mm %= value
    return ' '.join(result) if result else "0mm"
```