Parameters can (and in nf-core usually are) evaluated against a schema of valid options, this is somewhat defined via the schema https://github.com/nf-core/genomeassembler/blob/master/nextflow_schema.json#L246 and validation is based on the

schema_input.json

file, but genomeassembler is kind of lenient in input validation https://github.com/nf-core/genomeassembler/blob/master/assets/schema_input.json