Enable nullable reference types for MediaBrowser.Common

MediaBrowser.Common/Extensions/SplitStringExtensions.cs

@@ -21,7 +21,7 @@ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
  */
-#nullable enable
+
 #pragma warning disable CS1591
 #pragma warning disable CA1034
 using System;