The result of 'filterIsInstance' call is always empty

The inspection detects calls to Kotlin standard library functions filterIsInstance/filterIsInstanceTo, whose target type is not a subtype of the element type the filtering is called on.

Example:

    val list = listOf<Int>(1, 2, 3)
    val filteredList = list.filterIsInstance<Boolean>() // Empty result

Locating this inspection

By ID

Can be used to locate inspection in e.g. Qodana configuration files, where you can quickly enable or disable it, or adjust its settings.

FilterIsInstanceResultIsAlwaysEmpty

Via Settings dialog

Path to the inspection settings via IntelliJ Platform IDE Settings dialog, when you need to adjust inspection settings directly from your IDE.

Settings or Preferences | Editor | Inspections | Kotlin | Probable bugs

Inspection ID: FilterIsInstanceResultIsAlwaysEmpty

Suppressing Inspection

You can suppress this inspection by placing the following comment marker before the code fragment where you no longer want messages from this inspection to appear:

//noinspection FilterIsInstanceResultIsAlwaysEmpty

More detailed instructions as well as other ways and options that you have can be found in the product documentation:

IntelliJ IDEA 2025.3

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.3, Qodana for JVM 2025.3,

Last modified: 03 December 2025