How to create and apply cubemap to material in C#?

In my scene there is a gameobject (with Sphere mesh) and i want to apply a cubemap texture to its material. Create a 'New Material' with Cubemap/Skybox shader, and applied it to the game object. i referenced both the sphere object and the material in my C# script.

How can i create and apply a Cubemap to the sphere in code? because texture will be changing in runtime.

This is the exception i get (code runs on Android device):

 E/Unity: Material 'New Material (Instance)' with Shader 'Skybox/Cubemap' doesn't have a texture property '_MainTex'

  E/Unity: NullReferenceException: Object reference not set to an instance of an object
           at VrSphere.Start () [0x0006d] in <5baa6178d1f44f4fa9fe0697321ddb21>:0 

(VrSphere is the name of the C# script file)

Code:

 // referenced from Unity
 [SerializeField] private GameObject sphere;
 [SerializeField] private Material material;
 
 void Start()
     {
         if (sphere == null)
         {
             Debug.Log("sphere is null");
         }
         sphereRenderer = sphere.GetComponent<Renderer>();
         if (sphereRenderer == null)
         {
             Debug.Log("Sphere has no renderer");
             return;
         }
         testCubemapShader();
         sphereRenderer.material = material; // <-- throws exception here
 
     }
 
     private void testCubemapShader() {
         if (material == null) {
             Debug.Log("material is null, cannot set cube texture...");
             return;
         }
         material.mainTexture = getTestCubemap();
     }
 
     private Cubemap getTestCubemap() {
         int width = 500;
         int cubeFaceLength = width * width;
         Debug.Log(string.Format("FrameConfig.PanoramaWidth = {0}", FrameConfig.PanoramaWidth));
 
         Color[] negativeX = new Color[cubeFaceLength];
         Color[] negativeY = new Color[cubeFaceLength];
         Color[] negativeZ = new Color[cubeFaceLength];
         Color[] positiveX = new Color[cubeFaceLength];
         Color[] positiveY = new Color[cubeFaceLength];
         Color[] positiveZ = new Color[cubeFaceLength];
 
         for (int i = 0; i < cubeFaceLength; i++)
         {
             negativeX[i] = new Color(0, 0, 255);
             negativeY[i] = new Color(0, 255, 0);
             negativeZ[i] = new Color(255, 0, 0);
             positiveX[i] = new Color(100, 0, 55);
             positiveY[i] = new Color(0, 100, 55);
             positiveZ[i] = new Color(200, 0, 55);
         }
 
         Cubemap cube = new Cubemap(FrameConfig.PanoramaWidth, TextureFormat.ARGB32, false);
         cube.filterMode = FilterMode.Point;
         cube.Apply();
 
         cube.SetPixels(negativeX, CubemapFace.NegativeX);
         cube.SetPixels(negativeY, CubemapFace.NegativeY);
         cube.SetPixels(negativeZ, CubemapFace.NegativeZ);
         cube.SetPixels(positiveX, CubemapFace.PositiveX);
         cube.SetPixels(positiveY, CubemapFace.PositiveY);
         cube.SetPixels(positiveZ, CubemapFace.PositiveZ);
 
         Debug.Log(string.Format("cube name: {0}", cube.name));
         return cube;
     }