fix nullref with asset info when there's actually no asset info

Author: hybridherbst

Editor/Scripts/GLTFImporter.cs

@@ -969,7 +969,7 @@ private void CreateGLTFScene(GLTFImportContext context, out GameObject scene,
 			    scene = loader.LastLoadedScene;
 			    animationClips = loader.CreatedAnimationClips;
 
-			    _gltfAsset = loader.Root.Asset.ToString(true);
+			    _gltfAsset = loader.Root.Asset?.ToString(true);
 			    importer = loader;
 		    }
 	    }

Runtime/Scripts/GLTFSceneImporter.cs

@@ -203,6 +203,8 @@ public GameObject LastLoadedScene
 			get { return _lastLoadedScene; }
 		}
 
+		private bool AnyAnimationTimeNotIncreasing;
+
 		public TextureCacheData[] TextureCache => _assetCache.TextureCache;
 		public Texture2D[] InvalidImageCache => _assetCache.InvalidImageCache;
 		public MaterialCacheData[] MaterialCache => _assetCache.MaterialCache;
@@ -223,7 +225,7 @@ public GameObject LastLoadedScene
 		/// Whether to keep a CPU-side copy of the texture after upload to GPU
 		/// </summary>
 		/// <remaks>
-		/// This is is necessary when a texture is used with different sampler states, as Unity doesn't allow setting
+		/// This is necessary when a texture is used with different sampler states, as Unity doesn't allow setting
 		/// of filter and wrap modes separately form the texture object. Setting this to false will omit making a copy
 		/// of a texture in that case and use the original texture's sampler state wherever it's referenced; this is
 		/// appropriate in cases such as the filter and wrap modes being specified in the shader instead
@@ -1350,6 +1352,11 @@ protected virtual async Task ConstructScene(GLTFScene scene, bool showSceneObj,
 #else
 						Debug.Log(LogType.Warning, "glTF scene contains animations but com.unity.modules.animation isn't installed. Install that module to import animations.");
 #endif
+						if (AnyAnimationTimeNotIncreasing)
+						{
+							Debug.Log(LogType.Warning, $"Time of some subsequent animation keyframes is not increasing in {_gltfFileName} (glTF-Validator error ACCESSOR_ANIMATION_INPUT_NON_INCREASING)");
+						}
+						
 						CreatedAnimationClips = constructedClips.ToArray();
 					}
 				}

Runtime/Scripts/SceneImporter/ImporterAnimation.cs

@@ -205,8 +205,8 @@ private void SetTangentMode(Keyframe[] keyframes, int keyframeIndex, Interpolati
 					key.outTangent = 0;
 					break;
 				case InterpolationType.LINEAR:
-					key.inTangent = GetCurveKeyframeLeftLinearSlope(keyframes, keyframeIndex);
-					key.outTangent = GetCurveKeyframeLeftLinearSlope(keyframes, keyframeIndex + 1);
+					key.inTangent = GetCurveKeyframeLeftLinearSlope(keyframes, keyframeIndex, ref AnyAnimationTimeNotIncreasing);
+					key.outTangent = GetCurveKeyframeLeftLinearSlope(keyframes, keyframeIndex + 1, ref AnyAnimationTimeNotIncreasing);
 					break;
 				case InterpolationType.STEP:
 					key.inTangent = float.PositiveInfinity;
@@ -218,7 +218,7 @@ private void SetTangentMode(Keyframe[] keyframes, int keyframeIndex, Interpolati
 			keyframes[keyframeIndex] = key;
 		}
 
-		private static float GetCurveKeyframeLeftLinearSlope(Keyframe[] keyframes, int keyframeIndex)
+		private static float GetCurveKeyframeLeftLinearSlope(Keyframe[] keyframes, int keyframeIndex, ref bool anyNonCreasing)
 		{
 			if (keyframeIndex <= 0 || keyframeIndex >= keyframes.Length)
 			{
@@ -233,7 +233,7 @@ private static float GetCurveKeyframeLeftLinearSlope(Keyframe[] keyframes, int k
 				var k = keyframes[keyframeIndex];
 				k.time = keyframes[keyframeIndex - 1].time + Mathf.Epsilon + 1 / 100f;
 				keyframes[keyframeIndex] = k;
-				Debug.Log(LogType.Warning, "Time of subsequent animation keyframes is not increasing (glTF-Validator error ACCESSOR_ANIMATION_INPUT_NON_INCREASING)");
+				anyNonCreasing = true;
 				return float.PositiveInfinity;
 			}
 			return valueDelta / timeDelta;