<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def find_unique_values(input_file, property_name):
    '''
    Find unique values of a given property in a geojson file.

    Args
        input_file (str): File name.
        property_name (str): Property name.
    Returns
        List of distinct values of property. If property does not exist, it returns None.
    '''

    with open(input_file) as f:
        feature_collection = geojson.load(f)

    features = feature_collection['features']
    values = np.array([feat['properties'].get(property_name)
                       for feat in features])
    return np.unique(values)