TYPO3.Fluid

If the variable inside {} in Fluid is not found, Fluid displays nothing, so e.g.
{foo}
outputs nothing if foo does not exist.
If you have the following in your template (space inbetween brackets):
{ }
the output is nothing as well, but
{}
results in two brackets.
And this:
{ foo }
will output:
{ foo }

For example, this causes a problem in the kickstarter package: The syntax of the generated repository file is invalid, because the repository class does not contain anything between the opening and closing brackets ... which means these are not written at all.