Useless call on collection type

Reports filter… calls from the standard library on already filtered collections.

Several functions from the standard library such as filterNotNull() or filterIsInstance have sense only when they are called on receivers that have types distinct from the resulting one. Otherwise, such calls can be omitted as the result will be the same.

Remove redundant call quick-fix can be used to amend the code automatically.

Example:

  fun test(list: List<String>) {
      val x = list.filterNotNull() // quick-fix simplifies to 'list'
      val y = list.filterIsInstance<String>() // quick-fix simplifies to 'list'
  }

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.

UselessCallOnCollection

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

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 UselessCallOnCollection

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

IntelliJ IDEA 2025.2

Inspection Details
By default bundled with:	IntelliJ IDEA 2025.2, Qodana for JVM 2025.2,

Last modified: 18 September 2025