Currently in handling template parameters there is the option to use {{{1}}} which uses a value which is supplied or
{{{1|default}}}. In most instances this suffices.
However, in a series of nested templates, where the first template is a higher level template which in some use cases acts as pre-processor for lower level ones. you end up with constructions like this...
```
{{sub-template|required=foo|optional={{{optional|}}} }}
```
Which rather than passing an absence in the event of "optional" to the hgher level template, passes a "".
This as I understand it is working as designed, but makes it less clear for those trying to write, debug or maintain the templates.
On English Wikisource, I'd written https://en.wikisource.org/wiki/Template:Sanenull using parser functions to "force" known values for blank, empty and null values, in attempt to handle this situation.. I am strongly of the view that having {{{#sane:parameter}}} handling would be desirable. A further discussion as to what "sane" values to use as defaults for nulls or blanks could be had..
Alternatively for the use case above would some kind of {{{#pass:parameter}}} or {{#thru:paramater}}} be possible to provide? which would be intended to pass through certain parameters if they existed, or absent them from the call to a sub-template if they were not specified for the higher level one.
The intended construction (in a relevant template being)
```
{{sub-template|required=foo|optional ={{{#pass:optional}}} }}
```
If there's an actual value (or an explicit blank "") for optional specfied it gets passed, but if it's never specified, optional is NEVER in the list of parameters passed to the sub template, allowing the existing handling in respect of default values to be used in that sub template as at present.
Having functions like this would make writing 'nested' templates somewhat clearer....