Correct errors

Correct errors

Change the inner class to the static inner class.
Add explicit type casting.
Add the logic of null check to a variable.
Change the null parameter value to the empty interface object.
Remove unused class.
Add the logic of null check to a variable.

Change-Id: I53016f30b941e3677a0315ab8c3c176c35079f68
Signed-off-by: seokgil.kang <seokgil.kang@samsung.com>