Fix doBuildString for TopScope of NamespaceBinding

src/main/scala/scala/xml/NamespaceBinding.scala

@@ -72,7 +72,7 @@ case class NamespaceBinding(prefix: String, uri: String, parent: NamespaceBindin
     shadowRedefined(stop).doBuildString(sb, stop)
   }
 
-  private def doBuildString(sb: StringBuilder, stop: NamespaceBinding) {
+  protected def doBuildString(sb: StringBuilder, stop: NamespaceBinding) {
     if ((this == null) || (this eq stop)) return // contains?
 
     val s = " xmlns%s=\"%s\"".format(

src/main/scala/scala/xml/TopScope.scala

@@ -28,4 +28,5 @@ object TopScope extends NamespaceBinding(null, null, null) {
 
   override def buildString(stop: NamespaceBinding) = ""
   override def buildString(sb: StringBuilder, ignore: NamespaceBinding) = {}
+  override protected def doBuildString(sb: StringBuilder, stop: NamespaceBinding) = {}
 }

src/test/scala/scala/xml/XMLTest.scala

@@ -160,6 +160,23 @@ class XMLTest {
     for (n <- cuckoo \ "_") {
       assertEquals("http://cuckoo.com", n.namespace)
     }
+    val actual: String = new scala.xml.PrettyPrinter(80, 5).format(cuckoo)
+    val expected = """|<cuckoo xmlns="http://cuckoo.com">
+                      |     <foo/>
+                      |     <bar/>
+                      |</cuckoo>""".stripMargin
+    assertEquals(expected, actual)
+  }
+
+  @UnitTest
+  def namespacesWithNestedXmls: Unit = {
+    val foo = <f:foo xmlns:f="fooUrl"></f:foo>
+    val bar = <b:bar xmlns:b="barUrl">{foo}</b:bar>
+    val actual: String = new scala.xml.PrettyPrinter(80, 5).format(bar)
+    val expected = """|<b:bar xmlns:b="barUrl">
+                      |     <f:foo xmlns:f="fooUrl"></f:foo>
+                      |</b:bar>""".stripMargin
+    assertEquals(expected, actual)
   }
 
   @UnitTest