Make sure options is a hash

Author: rafaelfranca

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

@@ -687,12 +687,14 @@ def index_name_for_remove(table_name, options = {})
           index_name = index_name(table_name, options)
 
           unless index_name_exists?(table_name, index_name, true)
-            if options.has_key? :name
+            if options.is_a?(Hash) && options.has_key?(:name)
               options_without_column = options.dup
               options_without_column.delete :column
               index_name_without_column = index_name(table_name, options_without_column)
+
               return index_name_without_column if index_name_exists?(table_name, index_name_without_column, false)
             end
+
             raise ArgumentError, "Index name '#{index_name}' on table '#{table_name}' does not exist"
           end