GitHub API for comparing commits returns a null "sha" field when the only change to a file is to its file system permissions.

    "files": [
        {
            "sha": null,
            "filename": "echo-script",
            "status": "modified",
            "additions": 0,
            "deletions": 0,
            "changes": 0,
            "blob_url": "https://github.com/scott-fleischman/repo-change-file-permission/blob/77a95bbebeb78f4fb25c6a10c3c940b6fe1caa27/echo-script",
            "raw_url": "https://github.com/scott-fleischman/repo-change-file-permission/raw/77a95bbebeb78f4fb25c6a10c3c940b6fe1caa27/echo-script",
            "contents_url": "https://api.github.com/repos/scott-fleischman/repo-change-file-permission/contents/echo-script?ref=77a95bbebeb78f4fb25c6a10c3c940b6fe1caa27"
        }
    ]