Rails SQL Query if null

Rails SQL Query if null

References

Reference NO 1

http://stackoverflow.com/questions/15188761/rails-sql-query-if-null

Reference NO 2

http://stackoverflow.com/questions/4252349/rails-3-where-condition-using-not-null

Reference NO 3

http://edgeguides.rubyonrails.org/active_record_querying.html

Reference NO 4

http://blog.mitchcrowe.com/blog/2012/04/14/10-most-underused-activerecord-relation-methods

Reference NO 5

https://github.com/rails/rails/pull/4548

Reference NO 6

https://rails.lighthouseapp.com/projects/8994/tickets/6133?spam=1

Reference NO 7

http://blog.chrisblunt.com/rails-3-how-to-dynamically-build-complex-queries-with-composed-scopes/

Reference NO 8

#EANF#