code: public Coding getTag(String theSystem, String theCode) {
          for (Coding next : getTag()) {
            if (ca.uhn.fhir.util.ObjectUtil.equals(next.getSystem(), theSystem) && ca.uhn.fhir.util.ObjectUtil.equals(next.getCode(), theCode)) {
              return next;
            }
          }
          return null;
        }
docs: Returns the first tag (if any) that has the given system and code, or returns
  <code>null</code> if none