pfSense CE 2.8.1 + RESTAPI 2.6.5: dhcp static mapping creates empty <dhcpd><wan></wan> and causes crash on DNS Resolver Apply (related to #781) #787

Describe the bug

On pfSense CE 2.8.1 with the KEA DHCP backend and pfSense-pkg-RESTAPI-2.6_5, calling the v2 dhcp_server/static_mapping endpoint for a non-WAN interface (e.g. opt1) introduces an empty element into config.xml.

When the DNS Resolver configuration is applied (either via the GUI or via /api/v2/services/dns_resolver/apply while KEA is enabled), pfSense crashes.

This looks like a remaining instance of the problem that was addressed in #781 (“DHCPServer model initializing config for non-static interfaces”) since the v2.6.5 release notes say:

“Fixes an issue where the DHCPServer model could unintentionally initialize a DHCP server configuration for non-static interfaces. #781”

To Reproduce

1. Start from a clean config with KEA enabled and no <dhcpd><wan> block.
2. Add static mapping with POST /api/v2/services/dhcp_server/static_mapping endpoint
3. Download config.xml
4. Apply static mapping with POST /api/v2/services/dhcp_server/apply
5. In dns server add host override with: /api/v2/services/dns_resolver/host_override
6. Apply new host override with /api/v2/services/dns_resolver/apply

Expected behavior

• In the taken file in step 4. there should be no empty <dhcpd><wan></wan>
• The new DHCP end DNS entries should be applied with no errors.

Actual behavior

• Empty <dhcpd><wan></wan> is introduced in config.xml
• pfsense crashes with this error:

PHP ERROR: Type: 1, File: /etc/inc/util.inc, Line: 3961, Message: Uncaught TypeError: array_get_path(): Argument #1 ($arr) must be of type array, string given, called in /usr/local/pfSense/include/www/services_dhcp.inc on line 162 and defined in /etc/inc/util.inc:3961
Stack trace:
#0 /usr/local/pfSense/include/www/services_dhcp.inc(162): array_get_path()
#1 /etc/inc/system.inc(628): kea_earlydnsreg_mappings()
#2 /etc/inc/system.inc(660): system_hosts_entries()
#3 /etc/inc/services.inc(4983): system_hosts_generate()
#4 /usr/local/www/services_unbound.php(88): services_unbound_configure()
#5 {main}
thrown

pfSense Version & Package Version:

• pfSense Version: [e.g. pfSense 2.8.1]
• Package Version [e.g. v2.6_5]

Affected Endpoints:

• /api/v2/services/dhcp_server/static_mapping
• /api/v2/services/dns_resolver/apply

Additional context

I had to make this workaround to make thinks work:

I went to Services → DHCP Server → set WAN with a dummy range while keeping DHCP disabled , saved & applied

that fills <wan></wan> with content and avoids crash. But it's not clean...