`if defined(argument)` being used for optional scalar arguments

[multimeric]

For example, say I wanted to generate a WDL wrapper for the --lines flag for the unix tool head:

from wdlgen import Task

inp = Task.Command.CommandInput(
    name='lines',
    prefix='--lines',
    optional=True
)

print(inp.get_string())

This generates:

~{if defined(lines) then ("--lines " +  '"' + lines + '"') else ""}

However, what I want, based on this part of the spec is the much neater:

${"--lines=" + lines}

Or, including quotes:

${'--lines="' + lines + '"'}

How can I do this?

[illusional]

The optional scalar values should definitely simplify to:

${"--lines=" + lines}

I didn't realise string + null + string => null and hence totally empty, hence:

~{if defined(lines) then ("--lines " +  '"' + lines + '"') else ""}

And should be simplified as you suggested to:

${'--lines="' + lines + '"'}

I'll issue a PR for this soon.

[illusional]

(Future readers) Please see #4 (comment) for continuation of this.