This empty template is useful for introducing spaces or line breaks in places where they would normally be auto-removed.
To explain why this is needed, let's look at the following code first:
Paragraph 1
{{#if: condition |
Paragraph 2
}}
Paragraph 3
If all the condition is met, it works fine:
Paragraph 1 Paragraph 2 Paragraph 3
But if the condition isn't met, it will produce too much empty space, like this:
Paragraph 1 Paragraph 3
Let's try to improve on this by making sure we don't introduce empty paragraphs:
Paragraph 1 {{#if: condition |
Paragraph 2
}}
Paragraph 3
That works exactly as desired when the condition isn't met:
Paragraph 1 Paragraph 3
But... When the condition is met, it doesn't work as expected! It does this weird thing instead:
Paragraph 1 Paragraph 2 Paragraph 3
Why does that happen? It's because parser functions like #if strip all blanks (spaces and line breaks) that come before the first non-blank character, and after the last non-blank character. So the line breaks after {{#if: condition | are completely ignored!
This can be solved with the following trick. Note the use of the empty nowiki tag:
Paragraph 1 {{#if: condition | <nowiki></nowiki>
Paragraph 2
}}
Paragraph 3
The empty tag ends the blank auto-removal at the point it's inserted, so the line breaks that come after are not ignored.
It's tedious to write <nowiki></nowiki> every time, so you can instead use this blank template, which can fulfill the exact same purpose:
Paragraph 1 {{#if: condition | {{blank}}
Paragraph 2
}}
Paragraph 3
Result:
Paragraph 1 Paragraph 2 Paragraph 3