Check if the options value is present before to send the deprecation

message

activerecord/lib/active_record/connection_adapters/abstract/schema_statements.rb

@@ -629,11 +629,13 @@ module ActiveRecord
               index_options = options[:where] ? " WHERE #{options[:where]}" : ""
             end
           else
+            if options
               message = "Passing a string as third argument of `add_index` is deprecated and will" +
                 " be removed in Rails 4.1." +
                 " Use add_index(#{table_name.inspect}, #{column_name.inspect}, unique: true) instead"
 
               ActiveSupport::Deprecation.warn message
+            end
 
             index_type = options
           end