diff --git a/src/appdb.js b/src/appdb.js
index 52071a000..b3ddc35e2 100644
--- a/src/appdb.js
+++ b/src/appdb.js
@@ -104,7 +104,11 @@ function postProcess(result) {
         if (envNames[i]) result.env[envNames[i]] = envValues[i];
     }
 
-    result.error = safe.JSON.parse(result.errorJson) || { message: result.errorJson }; // make legacy error messages are JSON
+    if (result.errorJson === null) {
+        result.error = null;
+    } else {
+        result.error = safe.JSON.parse(result.errorJson) || { message: result.errorJson }; // make legacy error messages are JSON
+    }
     delete result.errorJson;
 
     result.taskId = result.taskId ? String(result.taskId) : null;