diff --git a/app/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java b/app/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
index 256590250..9566b1838 100644
--- a/app/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
+++ b/app/src/main/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactory.java
@@ -12,6 +12,8 @@
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
+ *
+ * From 0eb681b, adapted for Gadgetbridge to support null labels.
  */
 
 package com.google.gson.typeadapters;
@@ -19,6 +21,7 @@ package com.google.gson.typeadapters;
 import com.google.errorprone.annotations.CanIgnoreReturnValue;
 import com.google.gson.Gson;
 import com.google.gson.JsonElement;
+import com.google.gson.JsonNull;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonParseException;
 import com.google.gson.JsonPrimitive;
@@ -217,7 +220,7 @@ public final class RuntimeTypeAdapterFactory<T> implements TypeAdapterFactory {
      */
     @CanIgnoreReturnValue
     public RuntimeTypeAdapterFactory<T> registerSubtype(Class<? extends T> type, String label) {
-        if (type == null || label == null) {
+        if (type == null) {
             throw new NullPointerException();
         }
         if (subtypeToLabel.containsKey(type) || labelToSubtype.containsKey(label)) {
@@ -272,14 +275,14 @@ public final class RuntimeTypeAdapterFactory<T> implements TypeAdapterFactory {
                     labelJsonElement = jsonElement.getAsJsonObject().remove(typeFieldName);
                 }
 
-                if (labelJsonElement == null) {
+                if (labelJsonElement == null && !labelToDelegate.containsKey(null)) {
                     throw new JsonParseException(
                             "cannot deserialize "
                                     + baseType
                                     + " because it does not define a field named "
                                     + typeFieldName);
                 }
-                String label = labelJsonElement.getAsString();
+                String label = labelJsonElement != null ? labelJsonElement.getAsString() : null;
                 @SuppressWarnings("unchecked") // registration requires that subtype extends T
                 TypeAdapter<R> delegate = (TypeAdapter<R>) labelToDelegate.get(label);
                 if (delegate == null) {
@@ -319,7 +322,11 @@ public final class RuntimeTypeAdapterFactory<T> implements TypeAdapterFactory {
                                     + " because it already defines a field named "
                                     + typeFieldName);
                 }
-                clone.add(typeFieldName, new JsonPrimitive(label));
+                if (label != null) {
+                    clone.add(typeFieldName, new JsonPrimitive(label));
+                } else {
+                    clone.add(typeFieldName, JsonNull.INSTANCE);
+                }
 
                 for (Map.Entry<String, JsonElement> e : jsonObject.entrySet()) {
                     clone.add(e.getKey(), e.getValue());
diff --git a/app/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java b/app/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
new file mode 100644
index 000000000..520533241
--- /dev/null
+++ b/app/src/test/java/com/google/gson/typeadapters/RuntimeTypeAdapterFactoryTest.java
@@ -0,0 +1,66 @@
+package com.google.gson.typeadapters;
+
+import static org.junit.Assert.*;
+
+import com.google.gson.Gson;
+import com.google.gson.GsonBuilder;
+
+import org.junit.Test;
+
+public class RuntimeTypeAdapterFactoryTest {
+    private static final Gson GSON = new GsonBuilder()
+            .registerTypeAdapterFactory(RuntimeTypeAdapterFactory
+                    .of(Parent.class, "type")
+                    .registerSubtype(Child1.class, null)
+                    .registerSubtype(Child2.class, "child2")
+            )
+            .create();
+
+    @Test
+    public void testNullLabelSerialize() {
+        final Child1 child1 = new Child1("hello1");
+        final Child2 child2 = new Child2("hello2");
+
+        assertEquals("{\"field1\":\"hello1\",\"fieldParent\":\"fromChild1\"}", GSON.toJson(child1, Parent.class));
+        assertEquals("{\"type\":\"child2\",\"field2\":\"hello2\",\"fieldParent\":\"fromChild2\"}", GSON.toJson(child2, Parent.class));
+    }
+
+    @Test
+    public void testNullLabelDeserialize() {
+        final Parent child1 = GSON.fromJson("{\"field1\":\"hello1\",\"fieldParent\":\"fromChild1\"}", Parent.class);
+        assertTrue(child1 instanceof Child1);
+        assertEquals("fromChild1", child1.fieldParent);
+        assertEquals("hello1", ((Child1) child1).field1);
+
+        final Parent child2 = GSON.fromJson("{\"type\":\"child2\",\"field2\":\"hello2\",\"fieldParent\":\"fromChild2\"}", Parent.class);
+        assertTrue(child2 instanceof Child2);
+        assertEquals("fromChild2", child2.fieldParent);
+        assertEquals("hello2", ((Child2) child2).field2);
+    }
+
+    private static class Parent {
+        private final String fieldParent;
+
+        private Parent(final String fieldParent) {
+            this.fieldParent = fieldParent;
+        }
+    }
+
+    private static class Child1 extends Parent {
+        private final String field1;
+
+        private Child1(final String field1) {
+            super("fromChild1");
+            this.field1 = field1;
+        }
+    }
+
+    private static class Child2 extends Parent {
+        private final String field2;
+
+        private Child2(final String field2) {
+            super("fromChild2");
+            this.field2 = field2;
+        }
+    }
+}