Defect #35823

undefined method `+' for nil:NilClass

Added by Martin K 12 months ago. Updated 11 months ago.

Status:ClosedStart date:
Priority:NormalDue date:
Assignee:Go MAEDA% Done:


Target version:-
Resolution:Fixed Affected version:4.2.2


I am using latest Redmine SVN version, I am having trouble opening some issuses (some are OK, some cause error). This is what I get:

Started GET "/issues/4617" for xx.xx.xx.xx at 2021-08-28 09:07:21 +0200
Processing by IssuesController#show as HTML
  Parameters: {"id"=>"4617"}
  Current user: xxxx (id=3)
  Rendered issues/show.html.erb within layouts/base (Duration: 996.0ms | Allocations: 133997)
  Rendered layout layouts/base.html.erb (Duration: 996.6ms | Allocations: 134036)
Completed 500 Internal Server Error in 2302ms (ActiveRecord: 371.0ms | Allocations: 325712)

ActionView::Template::Error (undefined method `+' for nil:NilClass):
    11: <h3><%= l(:"label_#{watched_klass_name}_watchers") %> (<%= watched.watcher_users.size %>)</h3>
    13: <%= watchers_list(watched) %>

app/helpers/application_helper.rb:75:in `link_to_principal'
app/helpers/application_helper.rb:54:in `link_to_user'
app/helpers/watchers_helper.rb:54:in `block in watchers_list'
app/helpers/watchers_helper.rb:51:in `collect'
app/helpers/watchers_helper.rb:51:in `watchers_list'
app/controllers/issues_controller.rb:118:in `block (2 levels) in show'
app/controllers/issues_controller.rb:110:in `show'
lib/redmine/sudo_mode.rb:61:in `sudo_mode'
$ruby bin/about

sh: hg: command not found
sh: cvs: command not found
sh: bzr: command not found
  Redmine version                4.2.2.devel.21201
  Ruby version                   2.5.9-p229 (2021-04-05) [x86_64-linux]
  Rails version        
  Environment                    production
  Database adapter               PostgreSQL
  Mailer queue                   ActiveJob::QueueAdapters::AsyncAdapter
  Mailer delivery                smtp
  Subversion                     1.9.7
  Git                            2.14.3
Redmine plugins:
  periodictask                   4.1.0
  projects_table                 0.0.4
  redmine_editauthor             0.11.0
  redmine_impersonate            0.10.0
  redmine_timelog_timer          2.0.1
  sidebar_hide                   0.0.8

BTW: also happens if all plugins are disabled

35823.patch Magnifier (2.9 KB) Go MAEDA, 2021-09-04 10:24

Related issues

Related to Redmine - Feature #12795: View group members by non-admin users Closed

Associated revisions

Revision 21217
Added by Go MAEDA 11 months ago

Fix NoMethodError when generating a link to a locked user (#12795, #35823).


#1 Updated by Go MAEDA 12 months ago

Could you test if changing app/helpers/application_helper.rb as follows fixes the error?

diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index e3c858db4..b97b2fc98 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -70,6 +70,7 @@ module ApplicationHelper
       css_classes = 'group'
       name = h(principal.to_s)
+      css_classes = ''

     css_classes += " #{options[:class]}" if options[:class].present?

#2 Updated by Go MAEDA 12 months ago

  • Related to Feature #12795: View group members by non-admin users added

#3 Updated by Martin K 12 months ago

Sorry, still same error

#4 Updated by Mischa The Evil 12 months ago

Martin K wrote:

Sorry, still same error

I think I understand why. Please revert that change and try the following:

 app/helpers/application_helper.rb | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/app/helpers/application_helper.rb b/app/helpers/application_helper.rb
index e3c858db4..8f4ea5255 100644
--- a/app/helpers/application_helper.rb
+++ b/app/helpers/application_helper.rb
@@ -60,9 +60,10 @@ module ApplicationHelper
     case principal
     when User
       name = h([:format]))
+      css_classes = ''
       if || (User.current.admin? && principal.logged?)
         url = user_url(principal, :only_path => only_path)
-        css_classes = principal.css_classes
+        css_classes += principal.css_classes
     when Group
       name = h(principal.to_s)

@Go: this error is produced while rendering the issue user watchers on the issues show view. This is, besides the explicitly given code snippet, given by these lines in the stack trace:

app/helpers/watchers_helper.rb:54:in `block in watchers_list'
app/helpers/watchers_helper.rb:51:in `collect'
app/helpers/watchers_helper.rb:51:in `watchers_list'

Now if we go back to the error that is given, ActionView::Template::Error (undefined method `+' for nil:NilClass), we see that Redmine tries to send the + message to a nil object. The caller in that case is given by the first line (from the top) of the stack trace:

app/helpers/application_helper.rb:75:in `link_to_principal'

So, in the cases the error occurs css_classes is nil. Given that we're in the method link_to_principal and we're trying to send + to an object, I infer that css_classes should have been set1 prior to sending it this message. I look at the method and see that css_classes is set in several of the when branches of the case statement. We see that the case statement is passed the principal variable, so we need to figure out what branch we're on when the error occurs.
Now the value of principal is determined by what is passed along when link_to_principal was called. So we need to know what called link_to_principal when and with what arguments, thus we go back to the call stack and observe that it reads on the second line:

app/helpers/application_helper.rb:54:in `link_to_user'

Now, link_to_user has two execution paths based on the condition user.is_a?(User). link_to_user exits with the call to link_to_principal so we now know that the error occurs on a User object.

We then go back to the when User branch of the case statement in link_to_principal and determine that in the case that the error occurs, the assignment css_classes = principal.css_classes doesn't work as expected. Now, when we look at this code we see that this assignment is reached conditionally via the if-statement that it's wrapped in. The condition being: " || (User.current.admin? && principal.logged?)".

We now have reached the root cause of the issue: if ! or !(User.current.admin? && principal.logged?) we don't assign css_classes with principal.css_classes, hence is it nil by the time we send + to it on line 75.
This can as such be fixed by assigning css_classes with a blank string prior to the if-statement, and then subsequently add to that blank string (by sending it +=) the return value of principal.css_classes inside the if-statement.

Note: this error would also occur if the principal is something other than a User or Group object and link_principal is called and passed the :class option, which would then indeed be fixed by the patch you propose in note#1. However, I think that the CSS classes should be provided by the actual subclasses of Principal. They should implement a css_classes method to return this information as part of the model. As such:
  • should css_classes = 'group' be refactored into an assignment with the return value of a to-be-created Group#css_classes method
  • should be determined if link_principal should handle unknown Principals. Given that link_to_user prior to r21073 "handled" this by just returning a string representation of the principal, no class was needed. If link_principal is modeled after link_to_user prior to r21073, as it currently is, note#1 patch is not needed. However, in that case should the css_classes += " #{options[:class]}" if options[:class].present? assignment be done in both the User and Group branches of the case-statement.

Please let me know if more information is needed.

1 Be aware of the scope of local variables within case statements here also; i.e. case along with if, unless, for and while doesn't create a new scope in Ruby. See e.g. this question on StackOverflow and the references given therein.

#5 Updated by Mischa The Evil 12 months ago

  • Description updated (diff)

#6 Updated by Martin K 12 months ago

That helped, thanks! :)

#7 Updated by Go MAEDA 12 months ago

Thanks to the detailed explanation #35823#note-4 posted by Mischa, I understand what is causing the issue.

The following test catches the reported issue.

diff --git a/test/helpers/application_helper_test.rb b/test/helpers/application_helper_test.rb
index 06dd04b6a..2d7dd0fc5 100644
--- a/test/helpers/application_helper_test.rb
+++ b/test/helpers/application_helper_test.rb
@@ -1701,12 +1701,18 @@ class ApplicationHelperTest < Redmine::HelperTest

-  def test_link_to_user_should_link_to_locked_user_if_current_user_is_admin
+  def test_link_to_user_should_link_to_locked_user_only_if_current_user_is_admin
+    user = User.find(5)
+    assert user.locked?
     with_current_user User.find(1) do
-      user = User.find(5)
-      assert user.locked?
-      result = link_to("Dave2 Lopper2", "/users/5", :class => "user locked")
-      assert_equal result, link_to_user(user)
+      result = link_to('Dave2 Lopper2', '/users/5', :class => 'user locked assigned_to')
+      assert_equal result, link_to_user(user, :class => 'assigned_to')
+    end
+    with_current_user User.find(2) do
+      result = 'Dave2 Lopper2'
+      assert_equal result, link_to_user(user, :class => 'assigned_to')

#8 Updated by Go MAEDA 11 months ago

Here is a patch to fix this issue:

  • includes the fix #35823#note-4
  • includes the test #35823#note-7
  • implements Group#css_classes and link_to_principal uses the method
  • link_to_principal just returns a string representation for an unknown type principal. The behavior is the same as before r21073

#9 Updated by Martin K 11 months ago

should I set it to resolved or will somebody do it when it gets to SVN?

#10 Updated by Go MAEDA 11 months ago

  • Status changed from New to Closed
  • Assignee set to Go MAEDA
  • Resolution set to Fixed

Committed the fix in r21217 as a part of #12795.

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