Hello @Carlega,
As @Msquare_Automation suggests, if null comes at the start of the given URL (string), then using the substring() function works as you need.
But if you want to remove it from anywhere in the string, you can use the replace() function.
Try this formula.
{{replace("null79623029078/orders/null9d5cd3e19ba175cc0622cf41e206c5eanull"; "null"; emptystring)}}
Output
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