def _get_value_simple(doc, key):
    """
    Extracts a value from a nested set of dictionaries 'doc' based on
    a 'key' string.
    The key string is expected to be of the format 'x.y.z'
    where each component in the string is a key in a dictionary separated
    by '.' to denote the next key is in a nested dictionary.

    Returns the extracted value from the key specified (if found)
    Returns None if the key can not be found
    """
    split_key = key.split('.')
    if not split_key:
        return None

    value = doc
    for k in split_key:
        if isinstance(value, dict) and k in value:
            value = value[k]
        else:
            return None
    return value