Added empty string check (#15235)

* Added empty string check

* replaced tabs with spaces

replaced tabs with spaces

* Removed '(', ')' and enlarged if clause

* Added one space and removed an empty row

* removed is_null

Removed is_null check as static code analysis says that this variable cannot be null at this time

* compact form

* handle spaces

In case the sysName is " " (one space). Good to trim anyway.

---------

Co-authored-by: PipoCanaja <38363551+PipoCanaja@users.noreply.github.com>

app/Models/Device.php

@@ -180,12 +180,15 @@ class Device extends BaseModel
     {
         $hostname_is_ip = IP::isValid($this->hostname);
 
-        return SimpleTemplate::parse($this->display ?: \LibreNMS\Config::get('device_display_default', '{{ $hostname }}'), [
+        $return_value = SimpleTemplate::parse($this->display ?: \LibreNMS\Config::get('device_display_default', '{{ $hostname }}'), [
             'hostname' => $this->hostname,
             'sysName' => $this->sysName ?: $this->hostname,
             'sysName_fallback' => $hostname_is_ip ? $this->sysName : $this->hostname,
             'ip' => $this->overwrite_ip ?: ($hostname_is_ip ? $this->hostname : $this->ip),
         ]);
+
+        // in case the displayName is a string without any content, return hostname
+        return trim($return_value) ?: $this->hostname;
     }
 
     /**