[ecovacs] Handle invalid JSON responses properly

The API has differing responses depending on device type. If our
understanding of the JSON format differs from that of the API, make sure
to properly set the thing OFFLINE and to log a meaningful message.

Related to openhab#16187

Signed-off-by: Danny Baumann <dannybaumann@web.de>

bundles/org.openhab.binding.ecovacs/src/main/java/org/openhab/binding/ecovacs/internal/api/EcovacsApiException.java

@@ -27,6 +27,11 @@ public EcovacsApiException(String reason) {
         this(reason, false);
     }
 
+    public EcovacsApiException(String reason, Throwable cause) {
+        super(reason, cause);
+        isAuthFailure = false;
+    }
+
     public EcovacsApiException(String reason, boolean isAuthFailure) {
         super(reason);
         this.isAuthFailure = isAuthFailure;

bundles/org.openhab.binding.ecovacs/src/main/java/org/openhab/binding/ecovacs/internal/api/impl/EcovacsApiImpl.java

@@ -345,13 +345,18 @@ private <T> T handleResponseWrapper(@Nullable ResponseWrapper<T> response) throw
     }
 
     private <T> T handleResponse(ContentResponse response, Class<T> clazz) throws EcovacsApiException {
-        @Nullable
-        T respObject = gson.fromJson(response.getContentAsString(), clazz);
-        if (respObject == null) {
-            // should not happen in practice
-            throw new EcovacsApiException("No response received");
+        try {
+            @Nullable
+            T respObject = gson.fromJson(response.getContentAsString(), clazz);
+            if (respObject == null) {
+                // should not happen in practice
+                throw new EcovacsApiException("No response received");
+            }
+            return respObject;
+        } catch (IllegalStateException e) {
+            throw new EcovacsApiException("Failed to parse response '" + response.getContentAsString()
+                    + "' as data class " + clazz.getSimpleName(), e);
         }
-        return respObject;
     }
 
     private Request createAuthRequest(String url, String clientKey, String clientSecret,