Ensure genes of interest can be omitted

This goes both for the bed file input (key is `bed`) and the list of
gene names, `genes_of_interest`.

includes/expression/scripts/coverage.py

@@ -182,7 +182,6 @@ def main(
     raw: bool,
 ) -> None:
     if not bedfile and not genes:
-        print("Nothing to do")
         exit(0)
 
     coverage: dict[str, Coverage] = dict()

test/test_expression.yml

@@ -106,6 +106,24 @@
       contains:
         - "MT-CO2\t1.0\t1.0\t1.0"
 
+# The output files will be empty, but it should not crash
+- name: Test running the expression module without genes of interest or bed
+  tags:
+    - functional
+    - expression
+    - current
+  command: >
+    snakemake
+    --snakefile includes/expression/Snakefile
+    --workflow-profile test
+    --configfile test/data/config/expression.json
+    --config
+      pepfile=test/pep/expression.csv
+  exit_code: 0
+  files:
+    - path: SRR8615409/expression/coverage.csv
+    - path: SRR8615409/expression/coverage.normalized.csv
+
 - name: Check formatting of Snakemake files
   tags:
     - sanity