From 01f7bacce270b81239b83a693d1e4e6419752fc0 Mon Sep 17 00:00:00 2001
From: Sean Lilley <lilleyse@gmail.com>
Date: Wed, 4 Apr 2018 11:41:48 -0400
Subject: [PATCH 1/3] Added missing functions to ConstantSpline

---
 Source/Scene/ModelAnimationCache.js | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/Source/Scene/ModelAnimationCache.js b/Source/Scene/ModelAnimationCache.js
index 5a7c55ab800b..6f37b50a6768 100644
--- a/Source/Scene/ModelAnimationCache.js
+++ b/Source/Scene/ModelAnimationCache.js
@@ -114,6 +114,12 @@ define([
     ConstantSpline.prototype.evaluate = function(time, result) {
         return this._value;
     };
+    ConstantSpline.prototype.wrapTime = function(time) {
+        return 0.0;
+    };
+    ConstantSpline.prototype.clampTime = function(time) {
+        return 0.0;
+    };
 
     ModelAnimationCache.getAnimationSpline = function(model, animationName, animation, samplerName, sampler, input, path, output) {
         var key = getAnimationSplineKey(model, animationName, samplerName);

From 221df42ec8e31e85888b34349f46c06bd1677b36 Mon Sep 17 00:00:00 2001
From: Sean Lilley <lilleyse@gmail.com>
Date: Wed, 25 Apr 2018 15:17:38 -0400
Subject: [PATCH 2/3] Added test

---
 Specs/Scene/ModelSpec.js | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/Specs/Scene/ModelSpec.js b/Specs/Scene/ModelSpec.js
index fa5dd7b1f87e..86e819330104 100644
--- a/Specs/Scene/ModelSpec.js
+++ b/Specs/Scene/ModelSpec.js
@@ -1605,6 +1605,34 @@ defineSuite([
         expect(animations.update()).toEqual(false);
     });
 
+    it('animates a single keyframe', function() {
+        return Resource.fetchJson(animBoxesUrl).then(function(gltf) {
+            gltf.accessors['animAccessor_0'].count = 1;
+            gltf.accessors['animAccessor_1'].count = 1;
+
+            return loadModelJson(gltf).then(function(m) {
+                m.show = true;
+                var node = m.getNode('inner_box');
+                var time = JulianDate.fromDate(new Date('January 1, 2014 12:00:00 UTC'));
+                var animations = m.activeAnimations;
+                animations.add({
+                    name : 'animation_0',
+                    startTime : time
+                });
+
+                expect(node.matrix).toEqual(Matrix4.IDENTITY);
+                var previousMatrix = Matrix4.clone(node.matrix);
+
+                for (var i = 1; i < 4; ++i) {
+                    var t = JulianDate.addSeconds(time, i, new JulianDate());
+                    scene.renderForSpecs(t);
+                    expect(node.matrix).toEqual(previousMatrix);
+                }
+                primitives.remove(m);
+            });
+        });
+    });
+
     ///////////////////////////////////////////////////////////////////////////
 
     it('renders riggedFigure without animation', function() {

From de04ff466441d9e18ed5ad45db6254fc4fc64ac8 Mon Sep 17 00:00:00 2001
From: Sean Lilley <lilleyse@gmail.com>
Date: Wed, 25 Apr 2018 15:19:00 -0400
Subject: [PATCH 3/3] Updated CHANGES.md

---
 CHANGES.md | 1 +
 1 file changed, 1 insertion(+)

diff --git a/CHANGES.md b/CHANGES.md
index 117594f4d835..8d4469258581 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -29,6 +29,7 @@ Change Log
 * Fixed crash bug in PolylineCollection when a polyline was updated and removed at the same time. [#6455](https://github.com/AnalyticalGraphicsInc/cesium/pull/6455)
 * Fixed Imagery Layers Texture Filters Sandcastle example. [#6472](https://github.com/AnalyticalGraphicsInc/cesium/pull/6472).
 * Fixed a bug causing Cesium 3D Tilesets to not clip properly when tiles were unloaded and reloaded. [#6484](https://github.com/AnalyticalGraphicsInc/cesium/issues/6484)
+* Fixed crash when animating a glTF model with a single keyframe. [#6422](https://github.com/AnalyticalGraphicsInc/cesium/pull/6422)
 
 ### 1.44 - 2018-04-02