error: Command exit status: 255

[complexgenome]

I've a variant calling step using lancet, that is processed per chromosome. When I run it gives me error:

executor > local (3)
[17/7647ee] process > check (3) [ 0%] 0 of 24
Error executing process > 'check (1)'
executor > local (3)
[17/7647ee] process > check (3) [ 8%] 2 of 23, failed: 2
Error executing process > 'check (1)'

Caused by:
Process check (1) terminated with an error exit status (255)
Command exit status:
255

Command output:
(empty)

Command error:
Could not open tumor BAM file.

Please see following .nf file:

process check {

debug true

input:
    val chromosome

output: 
path("CHR"+{chromsome}+".lancet.vcf")

script:
"""

ml lancet

lancet --tumor tiny_tumor.sorted.markdup.recal.bam --normal tiny_normal.sorted.markdup.recal.bam --ref "Homo_sapiens_assembly38.fasta.gz" --reg "chr"$chromosome --num-threads 8 > "CHR"${chromosome}".lancet.vcf" 
"""

}
workflow {

chr=Channel.of( 1..22, 'X', 'Y' )

check(chr)
}

If I use command line lancet code runs fine for chr 1, 3:

lancet --tumor tiny_tumor.sorted.markdup.recal.bam --normal tiny_normal.sorted.markdup.recal.bam --ref "Homo_sapiens_assembly38.fasta.gz" --reg "chr"3 --num-threads 12 > "CHR"3".lancet.vcf"

lancet --tumor tiny_tumor.sorted.markdup.recal.bam --normal tiny_normal.sorted.markdup.recal.bam --ref "Homo_sapiens_assembly38.fasta.gz" --reg "chr"1 --num-threads 12 > "CHR"1".lancet.vcf"

I'm unable to debug what is going on and at which step. I understand the data are dummy and in the end 0 variants will be printed. I see no variants in CHR1 and CHR3 so far when performed on command line. However, this should be true when running through nextflow as well.