Our customer's main problem is the following:
How can we filter all Standard Issue Types (or Sub-Task Issue Types), which do not have an Original Estimate yet?
But there are other scenarios where we miss the possibility of searching for fields "that are still empty"
e.g., find all issues where there is no "Fixed in Build" (Text Field (< 255 characters) with Free Text Searcher)
or find all issues where there is no "Release Note" (Free Text Field (unlimited text) with Free Text Searcher)