how can i get the segment results by type

[ben-qiao]

i am using Samgeo and Samgeo2 for segment, how can i get the segment result by types. such as trees, buildings. from the API reference, Samgeo2 generate has return result which is "A list of dictionaries containing the generated masks". I tested it and only get None result. Did I get something wrong? here is the code:
`
from samgeo import SamGeo2

sam2 = SamGeo2(model_id="sam2-hiera-large", automatic=True)

image = '/mnt/data/qiaozh/samgeo/test/68.tif'

mask = "segment.tif"
result = sam2.generate(
image, mask, batch=True, foreground=True, erosion_kernel=(3, 3), mask_multiplier=255
)

print(result) // print None

shapefile = "segment.shp"
sam2.raster_to_vector(mask, shapefile)
`