default PlcValueType getPlcValueType() {
        return PlcValueType.NULL;
    }
Returns the "datatype" of the response one can expect from this tag.
I.e. The mapping between this string and the PlcValue datatype is handled in the ValueHandler class.

The contract is to return a String description of the datatype. This doesn't necessarily
define the PlcValue type but should be related.
i.e. returns "BOOL" -> PlcBOOL, returns "INT16" -> PlcINT
returning an empty string results in the default handler for that datatype to be evaluated.

@return The data type is generally parsed to the PlcTag class, if not a default datatype is returned.
plc4j/api/src/main/java/org/apache/plc4x/java/api/model/PlcTag.java