BYOND Environment This page contains an entry from the official DM Reference.

Variables that are not initialized have the value null. This value is distinct from 0 and "". If you compare it to these, using the == operator, it is not equal. However, in a numeric context (like a mathematical operation), null evaluates to 0 and in a text context (like insertion into a text expression), null evaluates to "". In a logical expression, null, 0, and "" evaluate to false and all other values are true.

In an embedded text expression, null behaves like "". That means, if you are expecting a variable to display a 0, you should explicitly initialize it to 0 rather than leaving it as null.