Implicit type conversion from `list` to `string`

[matthdsm]

Bug report

Expected behavior and actual behavior

When using .combine() on a value channel containing an array of 1, the array is implicitly converted into a string.

I suppose the type of the channel content shouldn't change after passing through a channel operator.

Steps to reproduce the problem

def Ch1 = Channel.of([
                    [id: "test", single_end: false, tag: "WES"], // meta
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/cram/sample1.sorted.cram", checkIfExists: true),
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/cram/sample1.sorted.cram.crai", checkIfExists: true),
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/genome/seq/GCA_000001405.15_GRCh38_full_plus_hs38d1_analysis_set_chr21.fna", checkIfExists: true),
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/genome/seq/GCA_000001405.15_GRCh38_full_plus_hs38d1_analysis_set_chr21.fna.fai", checkIfExists: true),
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/regions/roi_chr21.bed", checkIfExists: true),
                ])
                
def Ch2 = Channel.value([
                    file("https://github.com/nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/regions/genelists/genelist_chr21_per_exon.bed",checkIfExists:true)
                ])
                
Ch1.combine(Ch2).view()

// [[id:test, single_end:false, tag:WES], /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/cram/sample1.sorted.cram, /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/cram/sample1.sorted.cram.crai, /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/genome/seq/GCA_000001405.15_GRCh38_full_plus_hs38d1_analysis_set_chr21.fna, /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/genome/seq/GCA_000001405.15_GRCh38_full_plus_hs38d1_analysis_set_chr21.fna.fai, /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/regions/roi_chr21.bed, /nf-cmgg/test-datasets/raw/preprocessing/data/genomics/homo_sapiens/illumina/regions/genelists/genelist_chr21_per_exon.bed]

Program output

Environment

• Nextflow version: nextflow version 25.04.4.5950
• Java version:

openjdk 17.0.11 2024-04-16 LTS
OpenJDK Runtime Environment Zulu17.50+19-CA (build 17.0.11+9-LTS)
OpenJDK 64-Bit Server VM Zulu17.50+19-CA (build 17.0.11+9-LTS, mixed mode, sharing)

• Operating system: macOS
• Bash version: zsh 5.9 (arm64-apple-darwin24.0)

[bentsherman]

Possibly related: #5737, #6026