GeezerVison

Describe your change

• Add an algorithm?
• Fix a bug or typo in an existing algorithm?
• Add or change doctests? -- Note: Please avoid changing both code and tests in a single pull request.
• Documentation change?

Summary:
In conversions/binary_to_hexadecimal.py, bin_to_hexadecimal("-") and bin_to_hexadecimal(" - ") incorrectly returned "-0x0" instead of raising a ValueError.

When a negative sign is present, binary_str[1:] stripped the sign, leaving an empty string "". Because all(char in "01" for char in "") is vacuously true in Python, it bypassed validation, padded "" to "0000", and returned "-0x0".

This PR adds an emptiness check after stripping the optional negative sign:

if not binary_str or not all(char in "01" for char in binary_str):
    raise ValueError("Non-binary value was passed to the function")

and adds regression doctests for "-" and " - ".

Checklist

• I have read CONTRIBUTING.md.
• This pull request is all my own work -- I have not plagiarized.
• I know that pull requests will not be merged if they fail the automated tests.
• This PR only changes one algorithm file. To ease review, please open separate PRs for separate algorithms.
• All new Python files are placed inside an existing directory.
• All filenames are in all lowercase characters with no spaces or dashes.
• All functions and variable names follow Python naming conventions.
• All function parameters and return values are annotated with Python type hints.
• All functions have doctests that pass the automated testing.
• All new algorithms include at least one URL that points to Wikipedia or another similar explanation.
• If this pull request resolves one or more open issues, then the description above includes the issue number(s) with a closing keyword: "Fixes #ISSUE-NUMBER".