Redigerer Mal:If empty/dok (avsnitt)

===Rationale===
The MediaWiki parameter default function doesn't return the default value for empty parameters. That is, <code><nowiki>{{{logo|default.svg}}}</nowiki></code> does not return "default.svg" if the template was called like this: <code><nowiki>{{template|logo=}}</nowiki></code>.

The usual workaround for a single parameter is:
: <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |default.svg}}</nowiki></code>
: <nowiki>("If {{{logo}}} has a value, return it, else return "default.svg".")</nowiki>

But this becomes complex when several parameters are to be checked:
: <code><nowiki>{{#if:{{{logo|}}} |{{{logo}}} |{{#if:{{{image|}}} |{{{image}}} |{{#if:{{{picture|}}} |{{{picture}}} |default.svg}} }} }}</nowiki></code>
: <nowiki>("If {{{logo}}} has a value, return it; else if {{{image}}} has a value, return that; else if {{{picture}}} has a value, return that; else return "default.svg".")</nowiki>
In these cases, {{tlf|if empty}} produces the simpler syntax (as above):
: <code><nowiki>{{if empty |{{{logo|}}} |{{{image|}}} |{{{picture|}}} |default.svg}}</nowiki></code>

====Piping====
Parameters used with {{tlf|if empty}} must be [[Pipe (Unix)|pipe]]d&nbsp;– i.e. include the [[Vertical bar|vertical bar (pipe) symbol]] {{nowrap|("{{thinsp}}&#124;{{thinsp}}")}} as a trailing character&nbsp;– so that empty or undefined parameters aren't treated as text and returned incorrectly. Hence, for example, <code><nowiki>{{{logo|}}}</nowiki></code>, <code><nowiki>{{{image|}}}</nowiki></code> and <code><nowiki>{{{picture|}}}</nowiki></code> rather than {{param|logo}}, {{param|image}} and {{param|picture}} in the above examples.