VerifyError when using generic container in closure

@Grab('org.apache.pdfbox:pdfbox:2.0.28')
import org.apache.pdfbox.pdmodel.*
@Grab('io.vavr:vavr:0.10.4')
import io.vavr.control.Try
@CompileStatic
@POJO
class Bug {
    public static void main(String... args) {
        PDDocument doc = new PDDocument()
        extraPages().forEach {
            it.forEach(doc::addPage)
        }
    }
    static Try<Iterable<PDPage>> extraPages() {
        return Try.success([null]) // value present only to cause the iteration to proceed; NPE is the expected outcome here
    }
}

java.lang.VerifyError: Bad type on operand stack
Exception Details:
  Location:
    Bug$_main_closure1.doCall(Ljava/lang/Object;)Ljava/lang/Void; @11: invokedynamic
  Reason:
    Type 'java/lang/Object' (current frame, stack[1]) is not assignable to 'org/apache/pdfbox/pdmodel/PDDocument'
  Current Frame:
    bci: @11
    flags: { }
    locals: { 'Bug$_main_closure1', 'java/lang/Object' }
    stack: { 'java/lang/Iterable', 'java/lang/Object' }
  Bytecode:
    0000000: 2bc0 0024 2ab4 001c b600 2aba 003f 0000
    0000010: b900 4302 0001 ba00 5000 00b0          

	at Bug.main(Bug.groovy:16)

  public java.lang.Void doCall(java.lang.Object);
    descriptor: (Ljava/lang/Object;)Ljava/lang/Void;
    flags: (0x0001) ACC_PUBLIC
    Code:
      stack=2, locals=2, args_size=2
         0: aload_1
         1: checkcast     #36                 // class java/lang/Iterable
         4: aload_0
         5: getfield      #28                 // Field doc:Lgroovy/lang/Reference;
         8: invokevirtual #42                 // Method groovy/lang/Reference.get:()Ljava/lang/Object;
        11: invokedynamic #63,  0             // InvokeDynamic #0:accept:(Lorg/apache/pdfbox/pdmodel/PDDocument;)Ljava/util/function/Consumer;
        16: invokeinterface #67,  2           // InterfaceMethod java/lang/Iterable.forEach:(Ljava/util/function/Consumer;)V
        21: aconst_null
        22: invokedynamic #80,  0             // InvokeDynamic #1:cast:(Ljava/lang/Object;)Ljava/lang/Void;
        27: areturn
      LineNumberTable:
        line 17: 0
      LocalVariableTable:
        Start  Length  Slot  Name   Signature
            0      28     0  this   LBug$_main_closure1;
            0      28     1    it   Ljava/lang/Object;
    MethodParameters:
      Name                           Flags
      it