Summary

Drag and drop of issues on Kanban board is triggering a javascript error: Exception: Uncaught TypeError: Cannot read property 'top' of null

Steps to Reproduce

1. Create a sample project of Kanban type.
2. Visit the Kanban board for the first time, select any issue to Expand the Issue Details View in right sidebar.
3. Navigate away from the Kanban board and then return to the Kanban board by selecting it from the Board menu. The last viewed issue should still be active (selected), and Issue Details View should be expanded for this issue (Jira remembered this for us).
4. Try to DRAG any OTHER issue on the board by click and HOLD of the left mouse button. It is important to take this step right after opening the Kanban board, and not to left-click any issue beforehand on this screen.

Expected Results

The dragged issue should becomes selected in the Issue Detail view, and you can transition the issue by dragging it to another column.

Actual Results

A Javascript error pops-up

"Exception: Uncaught TypeError: Cannot read property 'top' of null"

pops up, and the issue can't be moved.

Notes/Workaround

1. The error is triggered only when Issue Details View in right sidebar is already expanded when user visit the Board. If it's collapsed (hidden), the no error will be thrown.
2. The error is triggered only when user tries to Drag issues that aren't shown in the Issue Details View, i.e. all issues except the currently selected one. If user tries to Drag currently selected issue, no error is thrown.
3. The error is thrown only if no issue selection events took place on the Board since user opened it. If any issue where explicitly selected by the user and the contents of the Issue Details View where reloaded, then no error will be shown.