[NUI] Fix build warning CA1062 (#2234)

[NUI] Fix build warning CA1062 (#2234)

* [NUI] Fix build warning CA1062

- Need to verify whether the argument is null
https://docs.microsoft.com/en-us/dotnet/fundamentals/code-analysis/quality-rules/ca1062

Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>
* [NUI] Add exception handling tag

- The <exception> tag lets you specify which exceptions can be thrown.

Signed-off-by: Seoyeon Kim <seoyeon2.kim@samsung.com>