What's causing "NoMethodError: undefined method `include?' for nil:NilClass"

Question

I have a Book model in my Rails application, with various properties (aka columns in the book db table). One of these properties is "ranking".

Recently, may app has started to throw NoMethodError: undefined method 'include?' for nil:NilClass for the following code:

def some_method(book, another_arg)
  return book.ranking unless book.ranking.blank?
  ...
end

However, it's not consistent. The vast majority of the time, accessing book.ranking works -- the error is thrown maybe 2-4% of the time. If I change the code to book[:ranking] or book['ranking'] instead of book.ranking, it works 100% of the time.

Any ideas?

P.S. This problem has popped up intermittently with other models and attributes... not just Book and the ranking attribute.

Answer 1

the book object is the one that is nil, not ranking. So having

return book.ranking unless book.nil?

should resolve the issue.

Answer 2

you should check if book is nil either

return book.ranking unless book.blank? and book.ranking.blank?

Answer 3

I would use try here:

book.try(:ranking)

If book or ranking is nil then nil will be returned.

Answer 4

You can do it also this way:

return book.ranking unless book and book.ranking

or with andand gem:

return book.ranking unless book.andand.ranking

Answer 5

there are a few ways to protect from nil-calls:

check with if:

return book.ranking if book

use &&/and:

return book && book.ranking

use try (in Ruby 1.9 or with Rails/ActiveSupport):

return book.try(:ranking)