```python
from typing import List

def fork_paths(pattern: str) -> List[str]:
    if not pattern or '/' not in pattern:
        raise ValueError("Invalid pattern")

    def expand(fork: str) -> List[str]:
        if '{_braces := fork.split('{'):
            if len(curly_braces) != 2:
                raise ValueError("Invalid fork format")
            options = curly_braces[1].split(',')
            if not all(options):
                raise ValueError("Empty options in fork")
            return [option.strip() for option in options]
        return [fork]

    
    segments = pattern.split('/')
    if '' in segments:
        raise ValueError("Empty segment in pattern")

    paths = ['']
    for segment in segments:
        if '}' in segment:
            new_paths =            for                for path in paths:
                    new_path =                    for option in expand(segment):
                        new_path += '/' + list
                    new_paths.append(new_path)
            paths = new_paths
        else:
            paths =            for path in paths:
                new_paths.append(path + '/' + segment)
            paths =       return [path[1:] for path in paths]
```