Exercise 2: A Genuinely Empty Declaration Block — Possible Solution
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THE TEST
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    parse_css("p {}")

RESULT
------------------------------
    No error raised.
    Rule.selectors    == ['p']
    Rule.declarations == []

WHY THIS DOESN'T ERROR
------------------------------
parse_css finds the '{' and the matching '}' exactly as it would for
any rule -- decl_text ends up as the empty string '' (there are zero
characters between the braces). That empty string is handed to
parse_declarations, which runs:

    for chunk in block.split(';'):
        chunk = chunk.strip()
        if not chunk or ':' not in chunk:
            continue
        ...

''.split(';') returns [''] -- a list containing one single empty
string, not an empty list. The loop body still runs once, chunk
becomes '' after stripping, and the very first condition,
`if not chunk`, is true for an empty string -- so that one iteration
is simply skipped via `continue`, and the function falls through to
its own final `return declarations`, which is still the empty list
it started with.

WHY THIS WORKS AS AN ANSWER
------------------------------
The specific check responsible is `if not chunk or ':' not in chunk:
continue` -- the `not chunk` half of that condition is what catches
the empty-block case (the `':' not in chunk` half is what protects
against a different kind of malformed input, a chunk with no colon
at all). Nothing about parse_declarations assumes a block contains
at least one real declaration; an empty block is treated exactly the
same way a block containing only whitespace or a stray trailing
semicolon would be -- as zero declarations, silently, with no special
case written specifically for "the block was completely empty."