[unifi] Fix NullPointerException (openhab#17421)

* Fix NPE
* Null warning

Signed-off-by: Leo Siepel <[email protected]>

Author: lsiepel

bundles/org.openhab.binding.unifi/src/main/java/org/openhab/binding/unifi/internal/handler/UniFiPoePortThingHandler.java

@@ -89,7 +89,8 @@ private boolean initPoeEnableMode() {
         } else {
             final String channelConfigPoeEnableMode = (String) channel.getConfiguration()
                     .get(CHANNEL_ENABLE_PARAMETER_MODE);
-            poeEnableMode = channelConfigPoeEnableMode.isBlank() ? CHANNEL_ENABLE_PARAMETER_MODE_AUTO
+            poeEnableMode = channelConfigPoeEnableMode == null || channelConfigPoeEnableMode.isBlank()
+                    ? CHANNEL_ENABLE_PARAMETER_MODE_AUTO
                     : channelConfigPoeEnableMode;
             return true;
         }
@@ -139,7 +140,7 @@ protected State getChannelState(final UniFiSwitchPorts ports, final String chann
         return state;
     }
 
-    private <Q extends Quantity<Q>> State safeDouble(final String value, final Unit<Q> unit) {
+    private <Q extends Quantity<Q>> State safeDouble(@Nullable final String value, final Unit<Q> unit) {
         try {
             return value == null ? UnDefType.UNDEF : QuantityType.valueOf(Double.parseDouble(value), unit);
         } catch (final NumberFormatException e) {