Dwifslpreproc - Error: No diffusion gradient table found

Hello MRTrix experts,

My question is about preprocessing with preproc step. There is only one phase encoding direction available in my DTI data. Therefore, I am skipping the “Extracting the Reverse Phase-Encoded Images” and would like to continue with preproc step. I tried the following command:
dwifslpreproc Ax_DTI_30_den.mif AX_DTI_30_den_preproc.mif -nocleanup -rpe_none -eddy_options " --slm=linear --data_is_shelled"
However I receive an error “No diffusion gradient table found”. Attached please find the screenshot of terminal.
I’d appreciate any advice on this. How should I move on if our data has only one phase-encoding direction.!
Screenshot from 2021-03-09 15-06-46|690x376

I found a solution under other topic discussion in MRtrix community. I will share my finding here for those who might face the same problem in the future.
You need to add -fslgrad bvec bval into the command line to access diffussion gradient table.

dwifslpreproc input.mif output.mif -fslgrad (name of file).bvec (name of file).bval -nocleanup -pe_dir AP -rpe_none -eddy_options " --slm=linear --data_is_shelled"