Sort out root namespace names

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetNamespaceHeader.java

@@ -79,10 +79,10 @@ public class JetNamespaceHeader extends JetReferenceExpression {
         return nameIdentifier == null ? "" : nameIdentifier.getText();
     }
 
-    @Nullable
+    @NotNull
     public Name getNameAsName() {
         PsiElement nameIdentifier = getNameIdentifier();
-        return nameIdentifier == null ? null : Name.identifier(nameIdentifier.getText());
+        return nameIdentifier == null ? JetPsiUtil.ROOT_NAMESPACE_NAME : Name.identifier(nameIdentifier.getText());
     }
 
     public boolean isRoot() {

compiler/frontend/src/org/jetbrains/jet/lang/psi/JetPsiUtil.java

@@ -40,6 +40,7 @@ import java.util.Set;
 public class JetPsiUtil {
 
     public static final Name NO_NAME_PROVIDED = Name.special("<no name provided>");
+    public static final Name ROOT_NAMESPACE_NAME = Name.special("<root namespace>");
 
     private JetPsiUtil() {
     }

compiler/frontend/src/org/jetbrains/jet/lang/resolve/JetModuleUtil.java

@@ -17,7 +17,7 @@
 package org.jetbrains.jet.lang.resolve;
 
 import org.jetbrains.jet.lang.psi.JetElement;
-import org.jetbrains.jet.lang.resolve.name.Name;
+import org.jetbrains.jet.lang.psi.JetPsiUtil;
 import org.jetbrains.jet.lang.resolve.scopes.JetScope;
 import org.jetbrains.jet.lang.types.NamespaceType;
 
@@ -27,6 +27,6 @@ import org.jetbrains.jet.lang.types.NamespaceType;
 public class JetModuleUtil {
     public static NamespaceType getRootNamespaceType(JetElement expression) {
         // TODO: this is a stub: at least the modules' root namespaces must be indexed here
-        return new NamespaceType(Name.special("<namespace_root>"), JetScope.EMPTY);
+        return new NamespaceType(JetPsiUtil.ROOT_NAMESPACE_NAME, JetScope.EMPTY);
     }
 }