```python
def long_word(sentence: str) -> str:
    """
    Return the longest word of a sentence, where any run of spaces separates two words.
    If two words are equally long, the one appearing first wins. A sentence holding no words returns empty text.
    """
    if not sentence:
        return ""
    
    # Split the sentence into words using split() which handles multiple spaces
    words = sentence.split()
    
    # Use max() with key=len to find the longest word
    # The lambda function ensures that words are compared by their length
    longest_word = max(words, key=len, default="")
    
    return longest_word
```