Siesta's getRow() is blowing up calling grid.getView() due to Modern returning an Ext.grid.Grid instead of Ext.grid.Panel.
This code has it working for me now.
getRow : function(grid, index) {
var domNode;
grid = this.normalizeComponent(grid);
if (grid) {
if (this.Ext().grid.Panel && grid instanceof this.Ext().grid.Panel) {
// if this is a locking grid, grab from locked grid
grid = grid.lockedGrid || grid;
domNode = grid && this.$(grid.getView().itemSelector, grid.getView().getEl().dom)[ index ];
return domNode && this.Ext().get(domNode);
}
else if (this.Ext().grid.Grid && grid instanceof this.Ext().grid.Grid) {
return grid.getViewItems()[index];
}
}
},