function unity_SpecCube0 doesn't work (or problem with skyBox)

Questions & Answers
1

I have these lines in my shader code.

half4 skyData = UNITY_SAMPLE_TEXCUBE(unity_SpecCube0, worldRefl);
half3 skyColor = DecodeHDR (skyData, unity_SpecCube0_HDR);
fixed4 c = 1 or fixed4 c = 0;
c.rgb = skyColor;

And after these lines skyColor is zero and my return color is black.
But I had a project before, with this shader, and everything was fine.
Also I downloaded sources from official documentation Unity - Manual: Vertex and fragment shader examples and it doesn’t work too.
I set up SkyBox in Window → Rendering → Lighting → Environment → SkyBox Material

2

In the end I gave up and began to use legacy->cubemap passing skybox of the current scene