diff --git a/src/cli.js b/src/cli.js
index 57ea787d..29bf728a 100755
--- a/src/cli.js
+++ b/src/cli.js
@@ -72,7 +72,7 @@ function startGeneration(argv) {
 }
 
 function addContribution(argv) {
-  const username = String(argv._[1])
+  const username = argv._[1] !== undefined ? String(argv._[1]) : undefined
   const contributions = argv._[2]
   // Add or update contributor in the config file
   return updateContributors(argv, username, contributions).then(data => {