Please see the minimized test:
-------------------------------------------
import java.dyn.*;
public class TestGeneric {
    public static <T> T foo(T param){
        return null;
    }
    public static void main(String argv[]) throws Exception {
        MethodHandle handle = MethodHandles.lookup().findStatic
            (TestGeneric.class, "foo",
                MethodType.methodType(Object.class, Object.class));
        try {
            String mh1 = (String) handle.invokeGeneric("");
        } catch (Throwable thr) {
            thr.printStackTrace();
        }
        try {
            Byte mh2 = (Byte) handle.invokeGeneric((Byte) 0);
        } catch (Throwable thr) {
            thr.printStackTrace();
        }
    }
}
-------------------------------------------

Its output is:
java.lang.RuntimeException: NYI
        at sun.dyn.InvokeGeneric.addReturnConversion(InvokeGeneric.java:147)
        at sun.dyn.InvokeGeneric.dispatchWithConversion(InvokeGeneric.java:129)
        at sun.dyn.FilterGeneric$F3.invoke_F2(FilterGeneric.java:573)
        at TestGeneric.main(TestGeneric.java:11)
java.lang.RuntimeException: NYI
        at sun.dyn.InvokeGeneric.addReturnConversion(InvokeGeneric.java:147)
        at sun.dyn.InvokeGeneric.dispatchWithConversion(InvokeGeneric.java:129)
        at sun.dyn.FilterGeneric$F3.invoke_F2(FilterGeneric.java:573)
        at TestGeneric.main(TestGeneric.java:16)