Hi, with the following parameters:

Quality control options
  skip_qc                   : true
  skip_fastqc               : true

trimming options
  save_trimmed              : true
  skip_trimming             : true

Assembler options
  user_assembly             : /path/to/assembly.fa.gz
  user_assembly_name        : user_assembly

Mapping options
  save_bam                  : true
  save_samtools             : true

Orf Caller options
  orf_caller                : transdecoder

I get:

Error executing process > 'NFCORE_METATDENOVO:METATDENOVO:COLLECT_STATS (user_assembly.transdecoder)'

Caused by:
  No such variable: read_trimlogs -- Check script '~/.nextflow/assets/nf-core/metatdenovo/./workflows/../modules/local/collect/stats/main.nf' at line: 64

It looks like line 64 is not conditioned! or read_trimlogs is missing a default empty value?

It sure does! Would you mind filing an issue: https://github.com/nf-core/metatdenovo/issues? A PR would be welcome too of course. If so, please add a test case.