Define whether the field can be null.
If set to 'true' and the extractor get no result, the entire class will be discarded.
返回:
whether the field can be null
默认值:
false
multi
public abstract boolean multi
已过时。since 0.4.2
Define whether the extractor return more than one result.
When set to 'true', the extractor return a list of string (so you should define the field as List).
Deprecated since 0.4.2. This option is determined automatically by the class of field.