SQL Server 2014 :: Like Statement With Parameters

I have a table :

Person(Id bigint , FirstName nvarchar(50) , LastName nvarchar(50),Address nvarchar(100))

and I have a sp for search data in "Person" table:

CREATE PROCEDURE SelectPerson
@First nvarchar(50) = NULL,
@Last nvarchar(50) = NULL,
@Address nvarchar(100) = NULL

[Code] ....

And there exists 500 record in Person.

I execute SelectPerson by this code:
"
DECLARE@return_value int
EXEC@return_value = [dbo].[SelectPerson ]
@First = 'ام',
@Last = NULL,
@Address= NULL

SELECT'Return Value' = @return_value
GO
"
but result don't has any rows.why?