join(remainder:true,by:[0,1]) operator (nf 24.10.4) returns a string instead of a tuple.

[lindenb]

Bug report

join(remainder:true,by:[0,1]) operator (nf 24.10.4)

see https://nextflow.slack.com/archives/C02T98A23U7/p1738431084540439

Expected behavior and actual behavior

Steps to reproduce the problem

in the following script

workflow {
	ch1 = Channel.of(["chr1",file("tmp1.bam"),"A"])
	ch2 = Channel.of(["chr1",file("tmp1.bam")])
	ch1.join(ch2,remainder:true,by:[0,1]).view()
}

the output, as expected, is a tuple
[chr1,/path/to/tmp1.bam, A]

but if the ch1 channel is by chance, filtered and then empty:

workflow {
	ch1 = Channel.of(["chr1",file("tmp1.bam"),"A"]).filter{it[0].equals("chrX")}
	ch2 = Channel.of(["chr1",file("tmp1.bam")])	
        ch1.join(ch2,remainder:true,by:[0,1]).view()
}

the output is a string

chr1

while I expected a tuple like:

[chr1,/path/to/tmp1.bam,null]

Environment

• Nextflow version: 24.10.4
• Operating system: .Linux