code: public String columnRemove(String key) {
          String resolvedKey = resolveColumnKey(key);
          columnMapCache.clear();
          return columnMap.remove(resolvedKey);
      }
docs: Removes the column value mapping for this key from this map if it is present.<p>
  
  Returns the value to which the map previously associated the key, or {@code null} if the map
  contained no mapping for this key. The map will not contain a String mapping for the
  specified key once the call returns.
  
  @param key key whose mapping is to be removed from the map.
  @return previous value associated with specified key, or {@code null} if there was no mapping
  for key.
  
  @throws NullPointerException if {@code key} is {@code null}.
  
  @see Map#remove(Object)