# Execute failed: webdriver must not be null **URL:** \ **Category:** Community Extensions\ **Tags:** palladian-selenium, bug\ **Created:** [August 23, 2021, 9:58pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545 "2021-08-23T21:58:46Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![sequoyah](https://forum-cdn.knime.com/user_avatar/forum.knime.com/sequoyah/32/30123_2.png) [@sequoyah](https://forum.knime.com/u/sequoyah)\ **Post date:** [August 23, 2021, 9:58pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/1 "2021-08-23T21:58:46Z")
Hi there fellow Knimers, I am scraping the number of fields of tennis clubs. In order to do so, I have a list with URL’s, which are used in the Start Webdrive node. Unfortunaly, I could not find any information on the forum with respect to the following error message that I get: _ERROR Start WebDriver 0:151:94:40:9 Execute failed: webDriver must not be null_ The error comes up randomly and when I re-execute the Loop End node, the loop just continues where it stopped. Therefore, I conclude that it is not a malfunctioning URL. Is someone maybe familiar with this failure? Thank you in advance for your reply! Kind regards, Sequoyah ![URL fout](https://forum-cdn.knime.com/uploads/default/original/3X/c/7/c7d0fca2fa5ac04e2f0efc66341e99be4ca13c20.png) ---
**Author:** ![qqilihq](https://forum-cdn.knime.com/user_avatar/forum.knime.com/qqilihq/32/50_2.png) [@qqilihq](https://forum.knime.com/u/qqilihq)\ **Post date:** [August 24, 2021, 8:47am UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/2 "2021-08-24T08:47:44Z")
Could you please send the workflow to [mail@seleniumnodes.com](mailto:mail@seleniumnodes.com) so that I can have a look? Thx, Philipp ---
**Author:** ![qqilihq](https://forum-cdn.knime.com/user_avatar/forum.knime.com/qqilihq/32/50_2.png) [@qqilihq](https://forum.knime.com/u/qqilihq)\ **Post date:** [August 25, 2021, 3:08pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/3 "2021-08-25T15:08:34Z")
Hi Sequoyah, I had a look at the workflow sent via email, yet, let me answer this here, as it is of general interest I think. 1. We will still need to figure out why the original `webDriver must not be null` happens after a few loop iterations. I currently only have a few assumptions, but we’ll need to dig deeper. 2. Generally, I advice against starting a new browser instance within loop iteration. This will cause quite some overhead for the start up time, and thus the workflow will run longer as necessary. Instead I suggest to start the browser using [Start WebDriver](https://nodepit.com/node/ws.palladian.nodes.selenium.start.StartWebDriverNodeFactory) **once** before the loop body. **Within** the loop, rather use a [Navigate](https://nodepit.com/node/ws.palladian.nodes.selenium.navigate.NavigateNodeFactory) node which opens the desired URL (instead of the “Start WebDriver”). This should fix your original issue. I will keep this thread updated once there’s a fix for (1). Hope this helps! –Philipp ---
**Author:** ![sequoyah](https://forum-cdn.knime.com/user_avatar/forum.knime.com/sequoyah/32/30123_2.png) [@sequoyah](https://forum.knime.com/u/sequoyah)\ **Post date:** [August 30, 2021, 10:03am UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/4 "2021-08-30T10:03:17Z")
Hi Philipp, I am sorry for the late reply, I had some days off 😁. Thank you for your clear explanation and time to look into my workflow. I will follow your advice. Have a nice week! Best, Sequoyah ---
**Author:** ![qqilihq](https://forum-cdn.knime.com/user_avatar/forum.knime.com/qqilihq/32/50_2.png) [@qqilihq](https://forum.knime.com/u/qqilihq)\ **Post date:** [September 1, 2021, 4:13pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/5 "2021-09-01T16:13:48Z")
**Update:** Today’s [4.8.2](https://seleniumnodes.com/changelog#version-4-8-2) release fixes the “webDriver must not be null” issue which was caused due to some concurrency issue. (thanks for spotting this, @sequoyah!) > **[Selenium Nodes — Changelog](https://seleniumnodes.com/changelog#version-4-8-2)** > > Overview of Selenium Nodes changes in each release. Yet, my general recommendation of above applies (start the browser only once, _before_ the loop). ---
**Author:** ![sequoyah](https://forum-cdn.knime.com/user_avatar/forum.knime.com/sequoyah/32/30123_2.png) [@sequoyah](https://forum.knime.com/u/sequoyah)\ **Post date:** [September 1, 2021, 4:26pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/6 "2021-09-01T16:26:32Z")
Great! Thank you very much for getting back to me @qqilihq! 😁 ---
**Author:** ![system](https://forum-cdn.knime.com/uploads/default/original/1X/ab3ccf34482a0329361734a18199390177204f15.png) [@system](https://forum.knime.com/u/system)\ **Post date:** [September 8, 2021, 4:27pm UTC](https://forum.knime.com/t/execute-failed-webdriver-must-not-be-null/35545/7 "2021-09-08T16:27:10Z")
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