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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:

def convert_ligatures(text_string):
    '''
    Coverts Latin character references within text_string to their corresponding unicode characters
    and returns converted string as type str.

    Keyword argument:

    - text_string: string instance

    Exceptions raised:

    - InputError: occurs should a string or NoneType not be passed as an argument
    '''
    if text_string is None or text_string == "":
        return ""
    elif isinstance(text_string, str):
        for i in range(0, len(LIGATURES)):
            text_string = text_string.replace(LIGATURES[str(i)]["ligature"], LIGATURES[str(i)]["term"])
        return text_string
    else:
        raise InputError("none type or string not passed as an argument")