You can compare directly to an empty string literal in the custom property formula.
For example, if your event property is called My Column, your custom event property formula would be:
```
text
if(.["My Column"] == "", "is empty", "is not empty")
LBKSThe key points from the docs:
- Empty string means the property was sent as `""` and appears in the UI as `(empty string)`. [[Falsy values](https://docs.mixpanel.com/docs/data-structure/property-reference/data-type#falsy-values)]
- Custom properties support the `==` and `!=` comparison operators for strings. [[Comparison operators](https://docs.mixpanel.com/docs/features/custom-properties#comparison-operators)]
So anywhere in a custom property formula, use `== ""` to check “is equal to (empty string)”, or `!= ""` to exclude empty strings.
