QIL improvement to common.sh: check for null return status from ECR call (#428)

* QIL improvement to common.sh: check for null return status from ECR call

* Simplify

Author: jljaco

scripts/lib/common.sh

@@ -149,7 +149,12 @@ is_public_ecr_logged_in() {
     # Base64 decode it
     # Read the "expiration" value
     local expiration_time
-    expiration_time=$(jq -r --arg url $public_ecr_url '.auths[$url].auth' ~/.docker/config.json | base64 -d | cut -d":" -f2 | base64 -d | jq -r ".expiration")
+    auth_string=$(jq -r --arg url $public_ecr_url '.auths[$url].auth' ~/.docker/config.json)
+
+    [ -z "$auth_string" ] && return 1
+    [ "$auth_string" = "null" ] && return 1
+
+    expiration_time=$(echo $auth_string | base64 -d | cut -d":" -f2 | base64 -d | jq -r ".expiration")
 
     # If any part of this doesn't exist, the user isn't logged in
     [ -z "$expiration_time" ] && return 1