Unsupported operand types in form.inc on line 2759 when adding a rule if there are no content types

Problem/Motivation

When I try to add a rule on a site with no content types (e.g.: minimal install profile), trying to select most events give me the following error:

An AJAX HTTP error occurred.
HTTP Result Code: 200
Debugging information follows.
Path: /system/ajax
StatusText: OK
ResponseText: 
( ! ) Fatal error: Unsupported operand types in /.../includes/form.inc on line 2759
Call Stack
#TimeMemoryFunctionLocation
10.0257268016{main}(  )../index.php:0
20.08792366256menu_execute_active_handler( ???, ??? )../index.php:21
30.08822367440call_user_func_array:{/.../includes/menu.inc:527}
( ???, ??? )../menu.inc:527
40.08822367672ajax_form_callback(  )../menu.inc:527
50.09102432304drupal_process_form( ???, ???, ??? )../ajax.inc:386
60.12303206144drupal_rebuild_form( ???, ???, ??? )../form.inc:973
70.14493280968form_builder( ???, ???, ??? )../form.inc:510
80.14833303320form_builder( ???, ???, ??? )../form.inc:1926
90.15243342408form_builder( ???, ???, ??? )../form.inc:1926
100.15263345864form_builder( ???, ???, ??? )../form.inc:1926
110.15293356192form_process_select( ???, ???, ??? )../form.inc:1870

Steps to reproduce

1. Download drupal-7.43, entity-7.x-1.7, rules-7.x-2.x-dev.
2. Install Drupal core with the minimal install profile, enable rules, rules_ui and all dependencies.
3. Log in as the super-administrator.
4. Go to admin/config/workflow/rules/reaction/add , enter:
   • Name = Test rule
   • Machine name = test_rule
   • Leave Tags empty.
   • React on event = Node -> After saving new content.
5. Expected behaviour: Can still add a rule, just can't restrict by type.
   Actual behaviour: error.

Proposed resolution

The error itself happens in the following line of code:

$element['#options'] = $empty_option + $element['#options'];

In this case, $empty_option is always set to an array, but $element['#options'] is NULL (or FALSE? — can't quite remember) because there are no content types for Rules' "Restrict by type" selectbox, and adding an array to a NULL / boolean causes the error.

Ensuring '#options' is an empty array instead of NULL or FALSE would fix this problem.

Remaining tasks

To be determined.

User interface changes

N/A.

API changes

N/A.

Data model changes

N/A.