Using entities and jobs

Below is my code, and I do not know what to do with the errors

 public class TestFinal : MonoBehaviour
 {
     [SerializeField] private Mesh mesh;
     [SerializeField] private Material material;
     public Texture2D _imageMap;
     [SerializeField] private bool useJobs;
     private NativeArray<Entity> entityArray;
     //public peerAtAudio Audiopeer;
     public int startScale;
     public int startMultiplier;
     public EntityManager entityManager;
     public EntityArchetype entityArchetype;
     public NativeArray<Entity> entityArray1;
     private void Start()
     {
         entityArchetype = entityManager.CreateArchetype(typeof(Translation), typeof(_bandComp), typeof(RenderMesh), typeof(LocalToWorld), typeof(Transform)); //entity that contains these
 
         entityArray1 = new NativeArray<Entity>(_imageMap.width * _imageMap.height, Allocator.Temp);//Allocator.Temp is chossen temp will be temporary to just establish the 2 entities
 
         Color[] pixels = _imageMap.GetPixels(0, 0, _imageMap.width, _imageMap.height);
 
         entityManager = World.Active.EntityManager;
 
 
         entityManager.CreateEntity(entityArchetype, entityArray1); //create entity in entity manager 
         int i = 0;
         for (int x = 0; x < _imageMap.width - 1; x++)
         {
             int iter = x * _imageMap.width;
             for (int y = 0; y < _imageMap.height - 1; y++)
             {
 
                 Color color1 = pixels[(iter) + y];
 
                 Entity entity = entityArray1[i]; //put each entity in the NativeArray 
 
                 entityManager.SetComponentData(entity, new Translation
                 {
                     Value = new float3(x, 0, y)
                 });
                 entityManager.SetComponentData(entity, new _bandComp
                 {
                     _band = UnityEngine.Random.Range(0, 8)
                 });
                 Material mat = new Material(material);
                 mat.color = color1;
                 entityManager.SetSharedComponentData(entity, new RenderMesh
                 {
 
                     mesh = mesh,
                     material = mat
                 });
                 i++;
             }
             i++;
         }
     }
     private void Update()
     {
         int size = _imageMap.width * _imageMap.height;
         ReallyToughParallelJob reallyToughParallelJob = new ReallyToughParallelJob
         { deltaTime = Time.deltaTime, entityMang = entityManager, entityArr = entityArray1 };
         JobHandle jobHandle = reallyToughParallelJob.Schedule(size, 100); // 100 means each job is handeling 100 components 
         jobHandle.Complete();
 
 
 
         /* ReallyToughParallelJob reallyToughParallelJob = new ReallyToughParallelJob { } 
          float startTime = Time.realtimeSinceStartup;
 
          NativeArray<float3> positionArray = new NativeArray<float3>(cubezList.Count, Allocator.TempJob);// in a regular game you will not need to instantiate this every time 
          NativeArray<float> moveYArray = new NativeArray<float>(cubezList.Count, Allocator.TempJob);
          for (int i = 0; i < cubezList.Count; i++)
          {
              positionArray[i] = cubezList[i].transform.position;
              moveYArray[i] = cubezList[i].moveY;
 
          }
          ReallyToughParallelJob reallyToughParallelJob = new ReallyToughParallelJob
          { deltaTime = Time.deltaTime, positionArr = positionArray, moveYArr = moveYArray };
          JobHandle jobHandle = reallyToughParallelJob.Schedule(cubezList.Count, 100); // 100 means each job is handeling 100 components 
          jobHandle.Complete();
          for (int i = 0; i < cubezList.Count; i++)
          {
              cubezList[i].transform.position = positionArray[i];
              cubezList[i].moveY = moveYArray[i];
          }
          positionArray.Dispose();
          moveYArray.Dispose();
          */
     }
 
 
 
     [BurstCompile]
     public struct ReallyToughParallelJob : IJobParallelFor
     {
         public NativeArray<Entity> entityArr;
         public EntityManager entityMang;
         public float deltaTime;
 
         public void Execute(int index)//index for multiple objects
         {
             Entity entity = entityArr[index];
             float3 val = entityMang.GetComponentData<Translation>(entity).Value;
             float3 val2 = new float3(1 * deltaTime, 0, 0);
             val = val + val2;
             entityMang.SetComponentData(entity, new Translation
             {
                 Value = val
             });
 
         }
     }
 }

I get these two errors:

NullReferenceException: Object reference not set to an instance of an object TestFinal.Start () (at Assets/tutorial/TestFinal.cs:34)

InvalidOperationException: ReallyToughParallelJob.entityMang is not a value type. Job structs may not contain any reference types. Unity.Jobs.LowLevel.Unsafe.JobsUtility.CreateJobReflectionData (System.Type type, Unity.Jobs.LowLevel.Unsafe.JobType jobType, System.Object managedJobFunction0, System.Object managedJobFunction1, System.Object managedJobFunction2) (at C:/buildslave/unity/build/Runtime/Jobs/ScriptBindings/Jobs.bindings.cs:96) Unity.Jobs.IJobParallelForExtensions+ParallelForJobStruct`1[T].Initialize () (at C:/buildslave/unity/build/Runtime/Jobs/Managed/IJobParallelFor.cs:23) Unity.Jobs.IJobParallelForExtensions.Schedule[T] (T jobData, System.Int32 arrayLength, System.Int32 innerloopBatchCount, Unity.Jobs.JobHandle dependsOn) (at C:/buildslave/unity/build/Runtime/Jobs/Managed/IJobParallelFor.cs:50) TestFinal.Update () (at Assets/tutorial/TestFinal.cs:81)