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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 as_string(value):
 """Convert a value to a Unicode object for matching with a query. None becomes the empty string. Bytestrings are silently decoded. """

    if six.PY2:
        buffer_types = buffer, memoryview  # noqa: F821
    else:
        buffer_types = memoryview

    if value is None:
        return u''
    elif isinstance(value, buffer_types):
        return bytes(value).decode('utf8', 'ignore')
    elif isinstance(value, bytes):
        return value.decode('utf8', 'ignore')
    else:
        return six.text_type(value)