code: public Long startProcess(Long processId, String masterRequestId, String ownerType,
              Long ownerId, Map<String,String> vars, Map<String,String> headers) throws Exception {
          return startProcess(processId, masterRequestId, ownerType, ownerId, vars, null, null, headers);
      }
docs: Start a process.
  @param processId
  @param masterRequestId
  @param ownerType
  @param ownerId
  @param vars Input parameter bindings for the process instance to be created
  @param headers
  @return the process instance ID