Cannot use getDeclaredFields() to retrieve fields of a Scala class

I'm trying to use a Java library (JOhm) with Scala and noticed it fails when the lib tries to read the fields of my Scala classes with something like model.getClass().getDeclaredFields().

Then I decided to try to do the same with simple examples in the Scala interpreter:

scala> import java.lang.reflect.Field;
import java.lang.reflect.Field

scala> class myClass(attribute1: String, attribute2: String, attribute3: String)
defined class myClass

scala> val myInstance = new myClass("value1", "value2", "value3")
myInstance: myClass = myClass@7055c39a

scala> myInstance.getClass().getDeclaredFields()
res0: Array[java.lang.reflect.Field] = Array()

Indeed, we get no field at all.

Now, what if I try this:

scala> class myClass2(attribute1: String, attribute2: String, attribute3: String) { override def toString = this.attribute1 }
defined class myClass2

scala> val myInstance2 = new myClass2("value1", "value2", "value3")
myInstance2: myClass2 = value1

scala> myInstance2.getClass().getDeclaredFields()
res1: Array[java.lang.reflect.Field] = Array(private final java.lang.String myClass2.attribute1)

So if use one of the fields in one of the class' methods, it is found by getDeclaredFields(). What am I missing here?