def _validate_translation_table_relations_dict(relations):
    """
    
    Parameters
    ----------
    relations : `dict` of (`str`, (`None`, `str`)) items
        Relations to validate.
    
    Returns
    -------
    validated_relations : `None`, `dict` of (`str`, `str`) items

    Raises
    ------
    TypeError
        - If an item's structure is incorrect.
    """
    validated_relations = None
    
    for key, value in relations.items():
        if not isinstance(key, str):
            raise TypeError(
                f'`relation` keys can be `str`, got {key.__class__.__name__}; {key!r}.'
            )
        
        if value is None:
            continue
        
        if not isinstance(value, str):
            raise TypeError(
                f'`relation` values can be `str`, got {value.__class__.__name__}; {value!r}.'
            )
        
        if (not key) or (not value):
            continue
        
        if validated_relations is None:
            validated_relations = {}
        
        validated_relations[key] = value
        continue
    
    return validated_relations