no need for special "nullopt" handling. using null instead

source/RobotAPI/libraries/aron/core/data/rw/reader/nlohmannJSON/NlohmannJSONReaderWithoutTypeCheck.cpp

@@ -163,17 +163,4 @@ namespace armarx::aron::data::reader
         i = input;
     }
 
-    bool
-    NlohmannJSONReaderWithoutTypeCheck::readNull(InputType& input)
-    {
-        try
-        {
-            const std::string e = input;
-            return e == "nullopt";
-        }
-        catch (...)
-        {
-            return false;
-        }
-    }
 } // namespace armarx::aron::data::reader

source/RobotAPI/libraries/aron/core/data/rw/reader/nlohmannJSON/NlohmannJSONReaderWithoutTypeCheck.h

@@ -70,6 +70,5 @@ namespace armarx::aron::data::reader
         void readString(InputType& input, std::string& i, Path& p) override;
         void readBool(InputType& input, bool& i, Path& p) override;
 
-        bool readNull(InputType& input) override;
     };
 } // namespace armarx::aron::data::reader