I am not sure about EASI's support of NANs, but this is well supported in Geomatica's Python API, which uses NumPy for custom raster processing. Furthermore, PCI will no longer be updating the EASI language going forward (with exception of supporting new PCI functions in future releases), so it is recommended that you consider switching to python in any case.
Here is how you can read in data with nan values in Geomatica's python API:
import numpy from pci.api import gobs, cts, datasource as ds # get the path to your .tif image with nan values nan_file = r'D:\example\my_nan_file.tif' # create a reader object with the channels from the input file you want to read in reader = ds.BasicReader(nan_file, ) # read the whole file read_raster = reader.read_raster(0, 0, reader.width, reader.height) # get the numpy array with the raster data nan_chan = read_raster.data
I hope this helps.