not use assert_not_nil in Errors#[]

r7593 etc. replaced Rails2 Errors#on.
Rails3 Errors#[] always return array.
So, Rails3 Errors#[] is always not nil.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/trunk@12070 e93f8b46-1217-0410-a6f0-8f06a7374b81

test/unit/issue_relation_test.rb

@@ -115,7 +115,7 @@ class IssueRelationTest < ActiveSupport::TestCase
           :relation_type => IssueRelation::TYPE_PRECEDES
         )
     assert !r.save
-    assert_not_nil r.errors[:base]
+    assert_not_equal [], r.errors[:base]
   end
 
   def test_validates_circular_dependency_of_subtask
@@ -166,7 +166,7 @@ class IssueRelationTest < ActiveSupport::TestCase
           :relation_type => IssueRelation::TYPE_BLOCKED
         )
     assert !r.save
-    assert_not_nil r.errors[:base]
+    assert_not_equal [], r.errors[:base]
   end
 
   def test_create_should_make_journal_entry