Calculations occasionally return errant all zero results

[davidfencik]

Calculations occasionally fail due to an unresolved promise. In lib/executor.js, the getPatientsById function needs to:
return await this.patientSource.findPatients(patientIdsList);
instead of:
return this.patientSource.findPatients(patientIdsList);

Otherwise null is occasionally returned which results in a query result with zero values for all populations.