Fix in compiler pass: cr.define() can export variable without assigned value

third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java

Index: third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java
diff --git a/third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java b/third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java
index 8ff3fb0a1405133424da35b7d6b6e67e5e8fc1de..c7f3c12daccb071f705a6a6a9c896653b3045a37 100644
--- a/third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java
+++ b/third_party/closure_compiler/runner/src/com/google/javascript/jscomp/ChromePass.java
@@ -295,7 +295,8 @@ public class ChromePass extends AbstractPostOrderCallback implements CompilerPas
                     !parent.isFunction()) {
                 if (parent.isVar()) {
                     if (parent.getParent() == this.namespaceBlock) {
-                        // It's a top-level exported variable definition.
+                        // It's a top-level exported variable definition (maybe without an
+                        // assignment).
                         // Change
                         //
                         //   var enum = { 'one': 1, 'two': 2 };
@@ -304,10 +305,14 @@ public class ChromePass extends AbstractPostOrderCallback implements CompilerPas
                         //
                         //   my.namespace.name.enum = { 'one': 1, 'two': 2 };
                         Node varContent = n.removeFirstChild();
-                        Node exprResult = IR.exprResult(
-                                    IR.assign(buildQualifiedName(n), varContent).srcref(parent)
-                                ).srcref(parent);
-
+                        Node exprResult;
+                        if (varContent == null) {
+                            exprResult = IR.exprResult(buildQualifiedName(n)).srcref(parent);
+                        } else {
+                            exprResult = IR.exprResult(
+                                        IR.assign(buildQualifiedName(n), varContent).srcref(parent)
+                                    ).srcref(parent);
+                        }
                         if (parent.getJSDocInfo() != null) {
                             exprResult.getFirstChild().setJSDocInfo(parent.getJSDocInfo().clone());
                         }