ElementConverter Element node should be nullable

[Tsuki]

Describe the bug
When not matched selector, the ElementConverter.convert is assigning (null,Selector)

To Reproduce
Steps to reproduce the behavior:

1. implement ElementConverter

class ExistConverter : ElementConverter<Boolean> {
  override fun convert(node: Element, selector: Selector): Boolean {
    return true
  }
}

3. @Selector("div.nav-previous > a", converter = ExistConverter::class)
4. Throw java.lang.IllegalArgumentException: Parameter specified as non-null is null: method kotlin.jvm.internal.Intrinsics.checkParameterIsNotNull, parameter node

Expected behavior
Element node remove @NotNull

Screenshots
N/A

Additional context
N/A