Tanka Issue

tk export fails on tanka versions=>0.14 in some scenarios:

I've provided 2 tanka environments (working and broken)

tk show and tk eval work on both.

tk export fails on the broken environment without a spec.json

Broken Example

$ tk --version
tk version v0.17.1

$ mkdir /tmp/broken-export
$ tk export /tmp/broken-export ./environments/broken

Error: evaluating jsonnet: RUNTIME ERROR: Field does not exist: app
	/tmp/tanka-export-issue/environments/broken/main.jsonnet:10:16-29	
	<std>:1366:30-34	thunk from <thunk from <function <anonymous>>>
	<std>:1361:20-21	thunk from <function <anonymous>>
	<std>:32:25-26	thunk from <function <anonymous>>
	<std>:32:16-27	function <anonymous>
	<std>:1361:8-22	function <anonymous>
	<std>:1366:20-35	thunk from <function <anonymous>>
	<std>:1353:10-11	function <isContent>
	<std>:1366:10-36	function <anonymous>
	<std>:(1363:34)-(1367:6)	
	<std>:(1363:34)-(1367:6)	
	<std>:1366:20-35	thunk from <function <anonymous>>
	<std>:1353:10-11	function <isContent>
	<std>:1366:10-36	function <anonymous>
	<std>:(1363:34)-(1367:6)	
	<std>:(1363:34)-(1367:6)	
	./environments/broken:(5:3)-(28:4)	function <noDataEnv>
	./environments/broken:30:1-16	$
	During evaluation

Working Example

The working example has a spec.json unnder https://github.com/nabadger/tanka-export-issue/tree/main/environments/working

$ tk --version
tk version v0.17.1

$ mkdir /tmp/working-export
$ tk export /tmp/working-export ./environments/working

Loading environments/working from /tmp/tanka-export-issue/environments/working/main.jsonnet

tk v0.13.0

Both versions work on v0.13.0 with or without a spec.json

Note, the order of params is different on tk export in this version.