If a template has no templatedata, we should attempt to extract the basic parameter names from the template and present them as-is (i.e. with basic text inputs and no labels or types or defaults etc.).
As is done by
https://en.wikipedia.org/wiki/User:%D7%A7%D7%99%D7%A4%D7%95%D7%93%D7%A0%D7%97%D7%A9/TemplateParamWizard.js
and https://de.wikipedia.org/wiki/Wikipedia:Technik/Skin/Gadgets/Vorlagenmeister
(Requested at https://en.wikipedia.org/wiki/User_talk:Samwilson#Template_parameters_wizard )
>>! In T54581#1271501, @Krinkle wrote:
> The TemplateData editor now supports scanning the template source code and inferring a list of parameter names to bootstrap the documentation editor.
>
> We can use the same logic server-side to provide a basic TemplateData object for templates lacking it. Possibly with a warning outputted alongside the object. Similar to how MediaWiki's query api communicates things like "warnings", "normalized", and "badrevids".