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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 _str_to_list(value, separator):
 """Convert a string to a list with sanitization."""

    value_list = [item.strip() for item in value.split(separator)]
    value_list_sanitized = builtins.list(filter(None, value_list))
    if len(value_list_sanitized) > 0:
        return value_list_sanitized
    else:
        raise ValueError('Invalid list variable.')