Discussion on fixing the `ObjectMapper.readValue` extension function problem(#399).

[k163377]

Currently, the ObjectMapper.readValue extension function may return null even if the type argument T is specified as non-null (#399).

This problem can be resolved by correcting the following

public inline fun <reified T> ObjectMapper.readValue(content: String): T =
  readValue(content, jacksonTypeRef<T>()) as T

// or

public inline fun <reified T> ObjectMapper.readValue(content: String): T =
  readValue(content, jacksonTypeRef<T>()).apply {
    if (this !is T) throw TODO("Some exception.")
  }

Here we want to determine what is the appropriate exception to be thrown(This discussion is a continuation from jackson-dev).

Specifications

In a strictly situational case, it is possible that is T could be false due to ObjectMapper problems.
For example, the deserializer may accidentally return null, or an inherited ObjectMapper may accidentally return an incorrect value.
In other words, the problem is not necessarily caused by invalid input.

Thus, a simple implementation of as T may result in both a NullPointerException and a ClassCastException.

Therefore, I personally think it is better to use the general exception defined in Jackson(JsonMappingException?) or the newly defined custom exception in kotlin-module.

Additional context

This fix does not solve the problem of StrictNullChecks not being applied to top-level collections.

[cowtowncoder]

My first thought based on discussion on mailing list is to consider InvalidNullException -- IllegalArgumentException is not quite it (I think I do understand why it seems initially like the thing).
And not NPE.

[k163377]

Let the discussion continue at #937.
This Issue is closed.