In a simple entity update situation, where there's an entity

class MyEntity {
  val id: Long? = null
  var prop1: String? = null
  var prop2: String? = null
// ...
  var propN: String? = null
}

and an update command:

class UpdateEntityCommand {
  val myEntityId: Long
  var prop1: String? = null
  var prop2: String? = null
// ...
  var propN: String? = null
}

the handler should only change property of the entity if corresponding property of the command is not

null

:

class MyHandler(private val repo: MyEntityRepository) {
  fun handle(command: UpdateEntityCommand) {
    with(repository.getOne(command.myEntityId)) {
      // (1)
      if (command.prop1 != null) prop1 = command.prop1
      // (2)
      command.prop2?.let { prop2 = it }
      // (3)
      ifNotNull(command.propN) { propN = it }
    }
  }
}

If all the properties are set using method (1) or (3), detekt is happy, if method (2) is used, detekt is complaining about

"ComplexMethod"

Should I report this to the issue tracker, or is it as it should be? If the latter, I wonder why?

This is an issue, so report it. The complexity of 1 and 2 are the same. And is

ifNotNull

an standard function? If so, it should be the same too.

No, not standard:

inline fun <T : Any, R> ifNotNull(input: T?, block: (T) -> R): R? = input?.let(block)