def sentence_case(text):
    """
    Converts the text to all lower-case, with the first character in the string
    being capitalized. This is a poor man's sentence case.
    Calling code should assume that we'll improve this algorithm over time to
    actually capitalize words after periods, etc.
    >>> sentence_case(None)
    >>> sentence_case('')
    ''
    >>> sentence_case('this is a test')
    'This is a test'
    >>> sentence_case('This is a test')
    'This is a test'
    >>> sentence_case('tHIS test')
    'This test'
    >>> sentence_case('Two sentences here. Yeah.')
    'Two sentences here. yeah.'
    """
    if not text:
        return text
    return text[0].upper() + text[1:].lower()