```python
from typing import List

def fork_paths(pattern: str) -> List[str]:
    if not isinstance(pattern, str):
        raise ValueError("Pattern must be a non-empty string")
    
    def is_valid_segment(segment):
        if segment == "":
            return False
        for char in segment:
            if char in " {}":
                return False
        return True
    
    def is_valid_option(option):
        if option == "":
            return False
        for char in option:
            if char not in " {}":
                return False
        return True
    
    def is_valid_pattern(pattern):
        if pattern == "":
            return False
        
        segments = pattern.split("/")
        
        for segment in segments:
            if not is_valid_segment(segment):
                return False
        
        for i, segment in enumerate(segments):
            if i > 0 and segment.startswith("{"):
                options = segment[1:-1].split(",")
                if len(options) == 0:
                    return False
                for option in options:
                    if not is_valid_option(option):
                        return False
        
        return True
    
    if not is_valid_pattern(pattern):
        raise ValueError("Pattern must be a non-empty string, an empty segment, an empty option, and a curly brace or comma sitting inside a literal segment or an option")
    
    def expand_segment(segment):
        if segment == "":
            return []
        
        if segment.startswith("{"):
            options = segment[1:-1].split(",")
            if len(options) == 0:
                return []
            
            result = []
            for option in options:
                result.extend(expand_segment(f"{segment}/{option}"))
            return result
        
        else:
            return [segment]
    
    def expand_pattern(pattern):
        segments = pattern.split("/")
        
        result = []
        for segment in segments:
            if segment.startswith("{"):
                options = segment[1:-1].split(",")
                if len(options) == 0:
                    result.append(segment)
                else:
                    for option in options:
                        result.extend(expand_pattern(f"{segment}/{option}"))
            else:
                result.extend(expand_segment(segment))
        
        return result
    
    return expand_pattern(pattern)
```