Why Nextflow pipeline don't find a file?

Question

I'm traying to launch a Nextflow pipeline, but it throws the following error:

ERROR ~ No signature of method: groovyx.gpars.dataflow.DataflowBroadcast.into() is applicable for argument types: (Script_dd34529ec87c0dd2$_runScript_closure3) values: [Script_dd34529ec87c0dd2$_runScript_closure3@39652a30]
Possible solutions: any(), find(), bind(java.lang.Object), print(java.io.PrintWriter), find(groovy.lang.Closure), any(groovy.lang.Closure)

The error is thrown by this part of the code:

Channel
    .fromFilePairs("$root/**/*.trk", size: -1) { it.parent.name }
    .into{ tractogram; tractogram_for_check } // [sid, tractogram.trk]

I think the problem is that it can't find the file, but it is in the correct folder and has the correct name and extension. How could I solve it? The GitHub source code of this pipeline.