Connector with variable of type Modelica.Units.SI.MassFraction.
Note that the mass fraction is in kg water vapor per total mass
of air, rathern than per kg of dry air.
This connector has been implemented to conditionally remove the mass fraction if the medium has only one species. While this could have been done using a vector of mass fractions with zero length, as is used in fluid connectors, this implemantation uses a scalar to avoid vectorized inputs and outputs of FMUs.
connector MassFractionConnector = Modelica.Units.SI.MassFraction;