Value emptiness in MVEL is different than a reference being null. Emptiness refers to, and is considered to be true, if any of the following conditions are true:

• a reference is null
• an array has a length of 0
• a collection has a size of 0
• a string has a length of 0
• a string has a length greater than 0 but is comprised only of whitespace
• a boolean value is false
• a numeric value is 0