added tests

com.unity.perception/Editor/Randomization/VisualElements/AssetSource/AssetListElement.cs

                 {
                     var optionProperty = m_Property.GetArrayElementAtIndex(optionsIndex + i);
                     optionProperty.objectReferenceValue = assets[i];
-                    m_Property.GetArrayElementAtIndex(i).floatValue = 0;
                 }
 
                 m_Property.serializedObject.ApplyModifiedProperties();

com.unity.perception/Runtime/Randomization/Randomizers/AssetSources/AssetSource.cs

         public T SampleAsset()
         {
             CheckIfInitialized();
-            return assetSourceLocation.LoadAsset<T>((int)(m_Sampler.Sample() * count));
+            return count == 0 ? null : assetSourceLocation.LoadAsset<T>((int)(m_Sampler.Sample() * count));
         }
 
         /// <summary>

com.unity.perception/Runtime/Randomization/Randomizers/AssetSources/LocalAssetSourceLocation.cs

         /// <summary>
         /// The list of local assets available from this source
         /// </summary>
-        [SerializeField] public List<Object> assets;
+        public List<Object> assets = new List<Object>();
 
         /// <inheritdoc/>
         public override int count => assets.Count;

com.unity.perception/Tests/Runtime/Randomization/AssetSourceTests/LocalAssetSourceTests.cs

 using NUnit.Framework;
 using UnityEngine;
 using UnityEngine.Perception.Randomization;
+using UnityEngine.Perception.Randomization.Randomizers.SampleRandomizers.Tags;
 
 namespace RandomizationTests.AssetSourceTests
 {
 
             public override void Preprocess(GameObject asset)
             {
-                throw new System.NotImplementedException();
+                asset.AddComponent<RotationRandomizerTag>();
             }
         }
 
             {
-                assetRole = null,
-                assetSourceLocation = new LocalAssetSourceLocation()
-            };
-
-            public AssetSource<Material> materialSource = new AssetSource<Material>
-            {
-                assetRole = null,
+                assetRole = new TestAssetRole(),
                 assetSourceLocation = new LocalAssetSourceLocation()
             };
         }
         public void TearDown()
         {
             Object.DestroyImmediate(m_TestObject);
+        }
+
+        [Test]
+        public void GetZeroCountWithoutThrowingException()
+        {
+            Assert.DoesNotThrow(() =>
+            {
+                var count = m_Behaviour.gameObjectSource.count;
+            });
+        }
+
+        [Test]
+        public void SampleFromEmptySourceReturnsNull()
+        {
+            Assert.IsNull(m_Behaviour.gameObjectSource.SampleAsset());
+            Assert.IsNull(m_Behaviour.gameObjectSource.SampleInstance());
         }
     }
 }