<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def string_to_decimal(value, strict=True):
 """ Return a decimal corresponding to the string representation of a number. @param value: a string representation of an decimal number. @param strict: indicate whether the specified string MUST be of a valid decimal number representation. @return: the decimal value represented by the string. @raise ValueError: if the string doesn't represent a valid decimal, while the argument ``strict`` equals ``True``. """

    if is_undefined(value):
        if strict:
            raise ValueError('The value cannot be null')
        return None

    try:
        return float(value)

    except ValueError:
        raise ValueError(
            'The specified string "%s" does not represent an integer' % value)