The null value corresponds to one of three different scenarios:
1. the absence of an attribute in a Ruletest Input pane or request message
2. the absence of data for an attribute in a Ruletest (the value zero counts as data)
3. a business object (supplied by an external application) that has an instance variable of null
A null value is different from an empty String (for String data types) or zero for numeric data types. An empty String is represented in a Ruletest as [] -- open then close square brackets. Any attribute value, including any empty strings, may be reset to null in a Ruletest by right-clicking the attribute and choosing Set to null. Mandatory attributes (property set in the Vocabulary) may not have a null value.
