code: protected Map<String, List<Object>> buildMutableAttributeMap(final Map<String, List<Object>> attributes) {
          final Map<String, List<Object>> mutableValuesBuilder = this.createMutableAttributeMap(attributes.size());
  
          for (final Map.Entry<String, List<Object>> attrEntry : attributes.entrySet()) {
              final String key = attrEntry.getKey();
              List<Object> value = attrEntry.getValue();
  
              if (value != null) {
                  value = new ArrayList<>(value);
              }
  
              mutableValuesBuilder.put(key, value);
          }
  
          return mutableValuesBuilder;
      }
docs: Do a deep clone of an attribute Map to ensure it is completley mutable.
  
  @param attributes Attribute map
  @return Mutable attribute map