diff --git a/src/docker.js b/src/docker.js
index 318cf0c2c..696280c9f 100644
--- a/src/docker.js
+++ b/src/docker.js
@@ -489,12 +489,9 @@ async function restartContainer(containerId) {
 }
 
 async function stopContainer(containerId) {
-    assert(!containerId || typeof containerId === 'string');
+    assert.strictEqual(typeof containerId, 'string');
 
-    if (!containerId) {
-        debug('No previous container to stop');
-        return;
-    }
+    debug(`stopContainer: stopping container ${containerId}`);
 
     const container = gConnection.getContainer(containerId);
 
@@ -510,9 +507,9 @@ async function stopContainer(containerId) {
 }
 
 async function deleteContainer(containerId) { // id can also be name
-    assert(!containerId || typeof containerId === 'string');
+    assert.strictEqual(typeof containerId, 'string');
 
-    if (containerId === null) return null;
+    debug(`deleteContainer: deleting ${containerId}`);
 
     const container = gConnection.getContainer(containerId);