code: private void deleteColumns(String storeName, String rowKey, Collection<String> colNames) {
          Map<String, List<String>> rowMap = m_columnDeletes.get(storeName);
          if (rowMap == null) {
              rowMap = new HashMap<>();
              m_columnDeletes.put(storeName, rowMap);
          }
          List<String> colList = rowMap.get(rowKey);
          if (colList == null) {
              colList = new ArrayList<>();
              rowMap.put(rowKey, colList);
          }
          colList.addAll(colNames);
          m_totalUpdates += colNames.size();
      }
docs: Add column deletions for all given column names.