Have the image tree allow a state with no selected image nor so selected tag.

static/js/controllers.js

@@ -302,7 +302,7 @@ function RepoCtrl($scope, Restangular, $routeParams, $rootScope) {
     var imageFetch = Restangular.one('repository/' + namespace + '/' + name + '/image');
     imageFetch.get().then(function(resp) {
       $scope.imageHistory = resp.images;
-      $scope.tree = new ImageHistoryTree(namespace, name, resp.images, $scope.currentTag, 
+      $scope.tree = new ImageHistoryTree(namespace, name, resp.images,
           $scope.getCommentFirstLine, $scope.getTimeSince);
 
       $scope.tree.draw('image-history-container');

static/js/graphing.js

@@ -4,7 +4,7 @@ var DEPTH_WIDTH = 132;
 /**
  * Based off of http://mbostock.github.io/d3/talk/20111018/tree.html by Mike Bostock (@mbostock)
  */
-function ImageHistoryTree(namespace, name, images, current, formatComment, formatTime) {
+function ImageHistoryTree(namespace, name, images, formatComment, formatTime) {
     /**
      * The namespace of the repo.
      */
@@ -20,21 +20,6 @@ function ImageHistoryTree(namespace, name, images, current, formatComment, forma
      */
     this.images_ = images;
 
-    /**
-     * The current tag.
-     */
-    this.currentTag_ = current.name;
-
-    /**
-     * The current image.
-     */
-    this.currentImage_ = current.image;
-
-    /**
-     * Counter for creating unique IDs.
-     */
-    this.idCounter_ = 0;
-
     /**
      * Method to invoke to format a comment for an image.
      */
@@ -44,6 +29,21 @@ function ImageHistoryTree(namespace, name, images, current, formatComment, forma
      * Method to invoke to format the time for an image.
      */
     this.formatTime_ = formatTime;
+
+    /**
+     * The current tag (if any).
+     */
+    this.currentTag_ = null;
+
+    /**
+     * The current image (if any).
+     */
+    this.currentImage_ = null;
+
+    /**
+     * Counter for creating unique IDs.
+     */
+    this.idCounter_ = 0;
 }
 
 
@@ -361,21 +361,27 @@ ImageHistoryTree.prototype.markPath_ = function(startingNode, isHighlighted) {
  * Sets the current tag displayed in the tree.
  */
 ImageHistoryTree.prototype.setTag_ = function(tagName) {
+    // Save the current tag.
     this.currentTag_ = tagName;
    
-    // Update the state of each existing node to no longer be highlighted.
     var imageByDBID = this.imageByDBID_;
+
+    // Update the state of each existing node to no longer be highlighted.
+    if (this.currentImage_) {
 	var currentNode = imageByDBID[this.currentImage_.dbid];
 	this.markPath_(currentNode, false);
+    }
 
-    // Find the new current image.
+    // Find the new current image (if any).
     this.currentImage_ = this.findImage_(function(image) {
-      return image.tags.indexOf(tagName) >= 0;
+      return image.tags.indexOf(tagName || '(no tag specified)') >= 0;
     });
 
     // Update the state of the new node path.
-    currentNode = imageByDBID[this.currentImage_.dbid];
+    if (this.currentImage_) {
+	var currentNode = imageByDBID[this.currentImage_.dbid];
 	this.markPath_(currentNode, true);
+    }
 
     // Ensure that the children are in the correct order.
     for (var i = 0; i < this.images_.length; ++i) {
@@ -432,6 +438,7 @@ ImageHistoryTree.prototype.update_ = function(source) {
   var diagonal = this.diagonal_;
   var tip = this.tip_;
   var currentTag = this.currentTag_;
+  var currentImage = this.currentImage_;
   var repoNamespace = this.repoNamespace_;
   var repoName = this.repoName_;
   var maxHeight = this.maxHeight_;
@@ -520,7 +527,10 @@ ImageHistoryTree.prototype.update_ = function(source) {
           if (d.collapsed) {
               return 'collapsed';
           }
-          return d.image.id == that.currentImage_.id ? 'current' : '';
+	  if (!currentImage) {
+	      return '';
+	  }
+          return d.image.id == currentImage.id ? 'current' : '';
       });
 
   // Ensure that the node is visible.