Uncaught TypeError: Cannot read property 'clearUndoStack' of undefined

[Enter steps to reproduce:]

1. ...
2. ...

**Atom**: 1.21.0 x64
**Electron**: 1.6.9
**OS**: Mac OS X 10.12.6
**Thrown From**: [tablr](https://github.com/abe33/atom-tablr) package 1.8.3

### Stack Trace

Uncaught TypeError: Cannot read property 'clearUndoStack' of undefined

```
At /Users/HALmob/.atom/packages/tablr/lib/table-element.js:1309

TypeError: Cannot read property 'clearUndoStack' of undefined
at HTMLElement.startCellEdit (/packages/tablr/lib/table-element.js:1309:36)
at Object.dblclick (/packages/tablr/lib/table-element.js:341:29)
at HTMLDivElement.listener (/packages/minimap/node_modules/atom-utils/lib/mixins/events-delegation.js:108:41)
```

### Commands

```
-8:08.3.0 tree-view:show (atom-workspace.workspace.scrollbars-visible-when-scrolling)
2x -7:59.9.0 existdb:run (input.hidden-input)
-6:06.3.0 open-on-github:file (ul.list-inline.tab-bar.inset-panel)
-4:35.4.0 core:confirm (input.hidden-input)
-3:55.6.0 core:save (input.hidden-input)
-3:51.9.0 existdb:run (input.hidden-input)
-3:41.2.0 existdb:upload-selected (span.name.icon.graph-icon.light-red)
-3:31.5.0 existdb:toggle-tree-view (div.tool-panel.tree-view)
-3:04.0 existdb:upload-selected (li.file.entry.list-item.selected)
```

### Non-Core Packages

```
atom-beautify 0.30.5
atom-live-server 2.1.2
autocomplete-xml 0.9.4
build 0.69.0
build-sassc 0.8.2
busy 0.7.0
busy-signal 1.4.3
emmet 2.4.3
existdb 0.6.0
file-icons 2.1.12
htmlhint 1.1.4
hyperclick 0.1.5
intentions 1.1.5
language-jsoniq 1.8.0
linter 2.2.0
linter-autocomplete-jing 0.8.2
linter-markdown 5.2.0
linter-ui-default 1.6.10
logo-file-icons 1.12.0
markdown-image-helper 1.0.4
merge-conflicts 1.4.5
minimap 4.29.7
open-html-in-browser 0.2.0
pigments 0.40.2
project-manager 3.3.5
tablr 1.8.3
todo-show 2.1.0
wordcount 2.10.4
xml-common-schemata 0.0.3
xml-tools 0.2.1
Zen 0.18.0
zotero-citations 0.19.1
```