Merged r23048 from trunk to 5.1-stable (#8539).

git-svn-id: https://svn.redmine.org/redmine/branches/5.1-stable@23049 e93f8b46-1217-0410-a6f0-8f06a7374b81

app/models/issue.rb

@@ -1018,7 +1018,7 @@ class Issue < ActiveRecord::Base
 
   # Returns true if this issue is blocked by another issue that is still open
   def blocked?
-    !relations_to.detect {|ir| ir.relation_type == 'blocks' && !ir.issue_from.closed?}.nil?
+    relations_to.any? {|ir| ir.relation_type == 'blocks' && ir.issue_from&.closed? == false}
   end
 
   # Returns true if this issue can be closed and if not, returns false and populates the reason

test/unit/issue_test.rb

@@ -2202,6 +2202,16 @@ class IssueTest < ActiveSupport::TestCase
     assert !blocking_issue.blocked?
   end
 
+  def test_blocked_should_not_raise_exception_when_blocking_issue_id_is_invalid
+    ir = IssueRelation.find_by(issue_from_id: 10, issue_to_id: 9, relation_type: 'blocks')
+    issue = Issue.find(9)
+    assert issue.blocked?
+
+    ir.update_column :issue_from_id, 0  # invalid issue id
+    issue.reload
+    assert_nothing_raised {assert_not issue.blocked?}
+  end
+
   def test_blocked_issues_dont_allow_closed_statuses
     blocked_issue = Issue.find(9)