What is the idiomatic way to deal with nullable values, referencing or converting them?

If I have a nullable type Xyz?, I want to reference it or convert it to a non-nullable type Xyz. What is the idiomatic way of doing so in Kotlin?

You have several options:

val something: Xyz? = createPossiblyNullXyz()

// access it as non-null asserting that with a sure call
// throws an exception if the value is null
val result1 = something!!.foo()

// access it only if it is not null using safe operator, 
// returning null otherwise
val result2 = something?.foo()

// access it only if it is not null using safe operator, 
// otherwise a default value using the elvis operator
val result3 = something?.foo() ?: differentValue

// null check it with `if` expression and then use the value, 
// similar to result3 but for more complex cases harder to do in one expression
val result4 = if (something != null) {
                   something.foo() 
              } else { 
                   ...
                   differentValue 
              }

// null check it with `if` statement doing a different action
if (something != null) { 
    something.foo() 
} else { 
    someOtherAction() 
}