Fix operator==

include/caosdb/protobuf_helper.h

@@ -58,16 +58,24 @@ public:
    * serialization.
    */
   inline auto operator==(const ProtoMessageWrapper<P> &other) const noexcept -> bool {
+    if (this->wrapped != nullptr && other.wrapped != nullptr) {
       return this->wrapped->SerializeAsString() == other.wrapped->SerializeAsString();
     }
+    // both nullptr?
+    return this->wrapped == other.wrapped;
+  }
 
   /**
    * Return true if the underlying Protobuf messages have a different
    * serialization.
    */
   inline auto operator!=(const ProtoMessageWrapper<P> &other) const noexcept -> bool {
+    if (this->wrapped != nullptr && other.wrapped != nullptr) {
       return this->wrapped->SerializeAsString() != other.wrapped->SerializeAsString();
     }
+    // only one is nullptr?
+    return this->wrapped != other.wrapped;
+  }
 
 protected:
   inline static auto CopyProtoMessage(P *wrapped) -> P * {