fterrier/kevin — pull request #144 by fterrier (2012-05-24 14:10:45+00:00)
Title: missing values are now treated as null values

before this patch, when an expression in a NDE referenced a missing value, the expression was not evaluated and the NDE value was automatically set to null.

this prevents writing an expression that checks for null values and returns (for example) an empty list in that case. to be able to test against null values in formulas, we just pass null and evaluate the formula nevertheless when a RDEValue is missing.