SynthesiserVoice called without any SynthesiserSound assign

I am developing an audio plugin based on the Synthesiser engine of Juce. When I launched the plugin, it makes directly a call to the SynthesiserVoice::renderNextBlock() without any previous call to a SynthesiserVoice::canPlay() method. Since my implementation depends on some assignations done in the SynthesiserVoice::canPlay() method, I have a bug.
Is there a way to define a default SynthesiserVoice that will be called directly (and that would do nothing)?