class CreateUserDTO(
        @Email @get:Email @setparam:Email
        var email: String
)

null

null as Array<String>?

class RequiredData(val firstField: String, val secondField: String)

interface SomeDataProvider {
    fun provide(): RequiredData
}

Assertions.assertThat()

someFun()

when

SpecificExceptions

object

null

object NoOperationMouseListener : MouseListener {
    ...
}

class MouseEventEmittingClass {
    var mouseListener: MouseListener = NoOperationMouseListener
}

java.util.Optional

filterNotNull()

Foo::myMember.annotations

/**
 * Returns the first element yielding the largest value of the given function or `null` if there are no elements.
 */
public inline fun <T, R : Comparable<R>> Iterable<T>.maxBy(selector: (T) -> R): T? {

Unit

void

is

when(x)

class A {
    companion object {
        const val name1 = "Antonel"
        const val name2 = StringBuilder("Antonel")
    }
}
error: const 'val' has type 'kotlin.text.StringBuilder /* = java.lang.StringBuilder */'. Only primitives and String are allowed