Board Thread:Support Requests - Getting Technical/@comment-38479212-20200919011313/@comment-9605025-20200919013139

Do you get that error message when you actually use the template? If not, then the only issue is that you didn't provide a default parameter value. When parameters are not specified (such as when viewing the template page itself), they are interpreted as text instead of parameters. So in this case, #expr would be trying to square the literal value which is not a number and thus cannot be squared.

There are two possible fixes to this: Let's say you want the default behavior to square "4.6". In, that case,
 * 1) Provide a default value
 * 2) Provide pre-defined output for when no value is provided

Now let's say that, instead, you don't want to assume a value but provide a message to the user that is a bit more meaningful than the default error message. In that case, you have two options. The first is this:

The alternative is this:

If you want it to fail silently (i.e. just don't show anything), then you can do something like this.