When opening the Population Editor for an expression whose roles play non-label types (nominalisations) and the substitution rules are missing or incomplete, the grid shows zero data columns — just a row-number column. The expression text displays correctly with two roles visible, but the grid is empty and unusable. There is no feedback about what is wrong, nor any way to fix the situation from the editor.\n\nFixed: the Population Editor now detects the empty grid condition and offers to open the Substitution Rules editor so the user can correct the issue. If the grid is still empty after editing (or in read-only mode), an appropriate warning message is shown and the editor closes gracefully instead of displaying a useless empty grid.