workflow: annottaion: hmm/kegg: db file not required if not set (issue #127)

workflow/rules/annotation.smk

@@ -166,7 +166,7 @@ rule annotation_barrnap:
 rule annotation_hmm_kegg:
     input:
         faa=os.path.join(RESULTS_DIR, "annotation/prodigal/{rtype}/{tool}/proteins.faa"),
-        hmm=os.path.join(DB_DIR, config["hmm"]["kegg"])
+        hmm=[os.path.join(DB_DIR, config["hmm"]["kegg"])] if config["hmm"]["kegg"] else []
     output:
         os.path.join(RESULTS_DIR, "annotation/hmm/kegg/{rtype}/{tool}/hmm.tblout")
     log: