Error in RSAGA::rsaga.env()

[raff-k]

Using the following function call

RSAGA::rsaga.env(path = "/opt/.../saga-gis-6.4.0/bin",
              root = "/opt/.../saga-gis-6.4.0") # ... stands for the full directory

I got the following error:

Verify specified path to SAGA command line program...
Found SAGA command line program. Search for not specified SAGA modules path...
Error in list.files(path = root, pattern = "libio_gdal", recursive = TRUE, :
argument "root" is missing, with no default

By debugging, the error is thrown in line 42
modules = rsaga.get.modules.path(saga.path = path) - due to the missing root-argument. If I set the root-argument in this function during debugging mode, I got a correct path.