code: public function getForcedQualificationCustomers()
      {
          if (is_null($this->cacheForcedRanks)) {
              /* get Customer IDs from DB to map ranks to Mage IDs instead of MLM IDs */
              $custIds = $this->getForcedCustomersIds();
              /* get all ranks with configuration parameters for all schemes */
              $ranks = $this->getCfgParamsByRanks();
              $this->cacheForcedRanks = [];
              foreach ($custIds as $item) {
                  $custId = $item[Customer::A_CUSTOMER_REF];
                  $ref = $item[Customer::A_MLM_ID];
                  $rankCode = $this->QUALIFIED_CUSTOMERS[$ref][1];
                  $cfgParamsWithSchemes = $ranks[$rankCode];
                  $this->cacheForcedRanks[$custId] = $cfgParamsWithSchemes;
              }
              /* compose map from customer IDs for quick search */
              $this->cacheForcedCustomerIds = array_keys($this->cacheForcedRanks);
          }
          return $this->cacheForcedRanks;
      }
docs: Load configuration data for customers with forced qualification.
  
  @return array