Side Chain input for an instrument (from host)

From this code I found, that implementing a side chain input in a plugin simply assumes the side chain input in second input, which is 0-based getAudioInput (1). When an instrument has no audio input, how should a host handle such side-chain input? Is the side-chain input for an instrument also always assumed to be the second input and then the first getAudioInput (0) simply has NULL buffers?

The sidechain is not index based. The bus type is BusTypes::kAux for a sidechain input.