undefined method `empty?' for nil:NilClass how to avoid it

Question

Hi Together I've got this code:

 @coursesFound = @user.available_courses
@courses = []

for course in @coursesFound do
  @courseInGroups = course.user_groups
  for group in @courseInGroups do
    @group = UserGroup.find group.id
    if @group.users.map { |u| u.id }.include? @user.id
      @courses << course
      break
    end
  end
end

# Wenn ein Kurs keiner Gruppe hinzugefügt wurde
if @courseInGroups.empty?
  @courses << course
end

on my debian vm it works fine but on my live system I got this error:

undefined method `empty?' for nil:NilClass

How can I avoid this?

@Felix more = other, your code doesn't include the `empty?` call any more. — Stefan, Aug 04 '15 at 09:36
apparently, `@courseInGroups` and therefore `course.user_groups` is `nil` — Stefan, Aug 04 '15 at 09:39

score 11 · Accepted Answer · answered Aug 04 '15 at 09:41

11

If this @coursesFound = @user.available_courses returns an empty activerecord relation.

Then this won't execute

for course in @coursesFound do
  @courseInGroups = course.user_groups
  for group in @courseInGroups do
    @group = UserGroup.find group.id
    if @group.users.map { |u| u.id }.include? @user.id
      @courses << course
      break
    end
  end
end

Which means when you get here @courseInGroups is nil

if @courseInGroups.empty?
  @courses << course
end

So your quick fix would be

if @courseInGroups && @courseInGroups.empty?
  @courses << course
end

answered Aug 04 '15 at 09:41

j-dexx

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2

Or you could replace `empty?` with `blank?` – Stefan Aug 04 '15 at 09:46
Yeah, that'd work. Clearly I'm a bit slow this morning :) – j-dexx Aug 04 '15 at 09:47
problem solved .. I have to put the `if @courseInGroups.empty? @courses << course end` in the first for – Felix Aug 04 '15 at 09:51

score 4 · Answer 2 · edited Nov 13 '21 at 14:11

4

You can use the try method to Avoid this error:

@courseInGroups.try(:empty?)

This won't throw an error if @courseInGroups was nil.

edited Nov 13 '21 at 14:11

Tomerikoo

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answered Aug 04 '15 at 09:44

bigsolom

2,309
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15

what does it do? mask it? – Kick Buttowski Jun 11 '19 at 20:39

score 2 · Answer 3 · edited Jun 11 '19 at 18:46

2

You need to properly initialize your object as well.

@courseInGroups = course.user_groups || []

You won't get nil:NilClass error any more if you initialize properly.

To get rid of nil:NilClass error you can use other answer. like try etc.

edited Jun 11 '19 at 18:46

Fred Willmore

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answered Aug 04 '15 at 10:44

Dipak Gupta

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Just in case "course.user_groups" will return an ActiveRecord relation, which is different from "[]" which is an array. Using "**Course.none**" (_Model.none_) would return an **empty** ActiveRecord relation, and that would be better instead of "[]". – Hugo Nov 26 '17 at 04:18

score 2 · Answer 4 · answered Dec 06 '17 at 18:41

And don't forget blank? when using rails. Here you find a good overview of all methods with or without rails.

I did not analyze your code, it's just for you, me and others that do not use this methods often, mix them up and then come here - just to remember: empty? is not blank?.

score 0 · Answer 5 · edited Nov 13 '21 at 14:02

0

You can put the ? before the dot of the empty:

if @courseInGroups?.empty

edited Nov 13 '21 at 14:02

Tomerikoo

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answered Nov 11 '21 at 17:17

Igor Cardoso

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undefined method `empty?' for nil:NilClass how to avoid it

5 Answers5