Fixing errors in Maven build

libraries/examples/browser-example/src/main/kotlin/sample/Hello.kt

@@ -5,6 +5,6 @@ import kotlin.browser.document
 fun myApp() {
     val element = document.getElementById("foo")
     if (element != null) {
-        element.appendChild(document.createTextNode("Some Dynamically Created Content!!!"))
+        element.appendChild(document.createTextNode("Some Dynamically Created Content!!!")!!)
     }
 }

libraries/kotlin-swing/src/main/kotlin/kotlin/swing/ActionListeners.kt

@@ -13,7 +13,7 @@ import java.awt.*
 inline fun actionListener(fn: (ActionEvent) -> Unit): ActionListener = FunctionActionListener(fn)
 
 private class FunctionActionListener(val fn: (ActionEvent) -> Unit) : ActionListener {
-    public override fun actionPerformed(e: ActionEvent?) {
+    public override fun actionPerformed(e: ActionEvent) {
         if (e != null) {
             (fn)(e)
         }

libraries/kotlin-swing/src/main/kotlin/kotlin/swing/Actions.kt

@@ -11,7 +11,7 @@ import javax.swing.Icon
  */
 fun action(text: String, description: String? = null, mnemonic: Int? = null, icon: Icon? = null, fn: (ActionEvent) -> Unit): Action {
     val answer = object: AbstractAction(text, icon) {
-        public override fun actionPerformed(e: ActionEvent?) {
+        public override fun actionPerformed(e: ActionEvent) {
             val event: ActionEvent = if (e != null) {
                 e
             } else {

libraries/kotlin-swing/src/main/kotlin/kotlin/swing/ChangeListeners.kt

@@ -16,7 +16,7 @@ import javax.swing.text.*
 inline fun changeListener(fn: (ChangeEvent) -> Unit): ChangeListener = FunctionChangeListener(fn)
 
 private class FunctionChangeListener(val fn: (ChangeEvent) -> Unit) : ChangeListener {
-    public override fun stateChanged(e: ChangeEvent?) {
+    public override fun stateChanged(e: ChangeEvent) {
         if (e != null) {
             (fn)(e)
         }

libraries/kotlin-swing/src/main/kotlin/kotlin/swing/Frames.kt

@@ -21,7 +21,7 @@ var JFrame.defaultCloseOperation: Int
 var JFrame.contentPane: Container?
     get() = getContentPane()
     set(value) {
-        setContentPane(value)
+        setContentPane(value!!)
     }
 
 var JFrame.title: String