Checking previous status != 'In Review' and then switched to 'In Review' - field expression now allowed for generic SObject line 33

ServiceRequestTrigger.java

public class ServiceRequestTrigger {
     private final Map<Id, Service_Request__c> oldMap;
     private final Map<Id, Service_Request__c> newMap;
     private final List<Service_Request__c> newObjs;
     private final Boolean isInsert;
     private final Boolean isUpdate;
     private final Boolean isDelete;
     private final Boolean isBulk;

     /**
     * The constructor
     *
     * @param xoldMap The old map from the trigger
     * @param xnewObj The list of new objects from the trigger
     * @param isBefore If the trigger is in before or after
     */
     public ServiceRequestTrigger(Map<Id, Service_Request__c> xoldMap, List<Service_Request__c> xnewObjs, Boolean isBefore) {
          oldMap = xoldMap;
          newObjs = xnewObjs;

          if (!isBefore && newObjs != null) {
               newMap = new Map<Id, Service_Request__c>(newObjs);
          }

          isDelete = (((newObjs == null || newObjs.isEmpty()) && isBefore) || ((newMap == null || newMap.isEmpty()) && !isBefore));
          isUpdate = ! (isDelete || oldMap == null || oldMap.isEmpty());
          isInsert = ! (isDelete || isUpdate);
          isBulk = (newObjs != null && newObjs.size() > 1) ? true : false;
     }

     public void doAwesomeness() {
          for (Service_Request__c srf: newObjs) {
            if (
                oldMap.get(srf.ID) != null && 
                oldMap.get(srf.ID).Status__c != srf.Status__c &&
                srf.Status__c == 'In Review'
            ) {
		  //do stuff
	    }
          }
     }
    /**
    * Method to initiate trigger logic
    *
    * @param oldMap The old map from the trigger
    * @param newObj The list of new objects from the trigger
    * @param isBefore If the trigger is in before or after
    */
     public static void processTrigger(Map<Id, Service_Request__c> oldMap, List<Service_Request__c> newObj, Boolean isBefore) {
          final ServiceRequestTrigger myTrigger = new ServiceRequestTrigger(oldMap, newObj, isBefore);

          if (!isBefore) {
               myTrigger.doAwesomeness();
          }
     }
}