Missing 'stdout' file when using slurm and singularity

[pouya-codes]

Hi, I want to use Nextflow for creating pipelines of singularity components which will be executed by slurm job scheduler.
I created a simple job to run just a single task:

#!/usr/bin/env nextflow

process createGroups {

  executor = 'slurm'
  queue = 'upgrade'
  memory = '10 GB'
  time = '30 min'
  cpus = 8
    """
    singularity run ...
    """
}

The job executes successfully and gives exit status 0, but Nextflow arises "Missing 'stdout' file" error. There is the full output:

Error executing process > 'createGroups'

Caused by:
  Missing 'stdout' file: .../work/89/449f849ffc77a967be91ed994da860/.command.out for process > createGroups

Command executed:
executor >  slurm (1)
[89/449f84] process > createGroups [100%] 1 of 1, failed: 1 ✘
Error executing process > 'createGroups'

Caused by:
  Missing 'stdout' file: .../work/89/449f849ffc77a967be91ed994da860/.command.out for process > createGroups

Command executed:

  singularity run ...

Command exit status:
  0

Command output:
  (empty)

Work dir:
  .../work/89/449f849ffc77a967be91ed994da860

Tip: when you have fixed the problem you can continue the execution adding the option `-resume` to the run command line

I couldn't find any solution to fix this error :(