#3178: impediments with an empty blocks list are invalid

app/models/impediment.rb

@@ -124,6 +124,7 @@ class Impediment < Task
   end
 
   def validate_blocks_list
+    errors.add :blocks_ids, :must_block_at_least_one_issue if relations_from.size == 0
     errors.add :blocks_ids, :can_only_contain_issues_of_current_sprint if relations_from.any?{|rel| rel.relation_type == IssueRelation::TYPE_BLOCKS && rel.issue_to.fixed_version != self.fixed_version }
   end
 end