allow empty settings (required for root directory)

lib/Service/SettingsService.php

@@ -101,7 +101,7 @@ class SettingsService {
 				$settings[$name] = $value = $this->attrs[$name]['validate']($value);
 			}
 			if (!array_key_exists($name, $this->attrs)
-				|| empty($value)
+				|| $value === null
 				|| $value === $this->attrs[$name]['default']
 			) {
 				unset($settings[$name]);
@@ -123,7 +123,7 @@ class SettingsService {
 		// use default for empty settings
 		$toBeSaved = false;
 		foreach ($this->attrs as $name => $attr) {
-			if (!property_exists($settings, $name) || empty($settings->{$name})) {
+			if (!property_exists($settings, $name)) {
 				$defaultValue = $attr['default'];
 				if (is_callable($defaultValue)) {
 					$settings->{$name} = $defaultValue($uid);

src/components/AppSettings.vue

@@ -9,7 +9,7 @@
 					v-model="settings.notesPath"
 					type="text"
 					name="notesPath"
-					:placeholder="t('notes', 'path to notes')"
+					:placeholder="t('notes', 'root directory')"
 					@change="onChangeSettingsReload"
 				><input type="submit" class="icon-confirm" value="">
 			</form>

tests/api/APIv1Test.php

@@ -181,6 +181,9 @@ class APIv1Test extends CommonAPITest {
 		], (object)[
 			'notesPath' => 'New-Test-Notes-Folder2',
 		], 'Update notesPath with path traversal check');
+		$this->updateSettings($settings, (object)[
+			'notesPath' => '',
+		], (object)[], 'Update notesPath with root directory');
 		$this->updateSettings($settings, (object)[
 			'fileSuffix' => 'illegal value',
 		], (object)[