def validate_key_value_pairs(string):
    """ Validates key-value pairs in the following format: a=b;c=d """
    result = None
    if string:
        kv_list = [x for x in string.split(';') if '=' in x]     # key-value pairs
        result = dict(x.split('=', 1) for x in kv_list)
    return result