Map values fetched with not-null assertion operator KT-W1034

Using the not-null assertion operator (!!) along with the index operator [] or the .get() method of a map type can result in a NullPointerException if the key is not present in the map. This is because Map.get() returns null if the key is not found. By using the not-null assertion operator, you are explicitly telling the compiler that the result will never be null, which can lead to a runtime exception if the assumption is incorrect.

To fix this issue we can use methods like map.getValue(), map.getOrDefault(), map.getOrElse(), or just index the map with [] without also coercing the value to be non-null.

Bad Practice

val value = map["nonExistentKey"]!!
val prop = value.someProperty // This will raise a `NullPointerException`

Recommended

val value = map["nonExistentKey"]
val prop = value?.someProperty