Attribute merging strategy that sums both attribute values when merging attributes. When merging two attributes,
attribute values that are not NumericAttrValues nor can't be directly converted to one are considered to be
NumericAttrValues with value 0.
Attribute merging strategy that sums both attribute values when merging attributes. When merging two attributes, attribute values that are not NumericAttrValues nor can't be directly converted to one are considered to be NumericAttrValues with value 0.
StringAttrValues whose value can be parsed to a double can be converted to a NumericAttrValue. BooleanAttrValues with value
falsecan be converted to a NumericAttrValue with value 0. BooleanAttrValues with valuetruecan be converted to a NumericAttrValue with value 1.