CompileStatic: @ClosureParams in @DelegatesTo doesn't work

import groovy.transform.CompileStatic
import groovy.transform.stc.ClosureParams
import groovy.transform.stc.FirstParam
import groovy.transform.stc.FromString

@CompileStatic
class Delegate {

  def <T2> void someFunctionName(Collection<T2> values, @ClosureParams(FirstParam.FirstGenericType) Closure<String> optionKey) {
  }

  static Delegate of(@DelegatesTo(Delegate) Closure c) {
    def d = new Delegate()
    c.delegate = d
    c()
    return d
  }
}

@CompileStatic
class App {

  List<Integer> someList

  Delegate datePicker = Delegate.of {
    someFunctionName(
      this.someList,
      // Here: Cannot find matching method java.lang.Object#toBigDecimal(). Please check if the declared type is correct and if the method exists.
      // But it should be known to be Integer
      // The code compiles when delegate.someFunctionName is used above
      { it.toBigDecimal().toString() },
    )
  }
}

new App()