You can use oclIsUndefined() in an OCL expression to test whether a value is either null or invalid.

Syntax

expression.oclIsUndefined() : Boolean

The operation returns true when expression is null or invalid. It returns false for a defined, valid value.

When to use it

Use oclIsUndefined() when your expression must treat both a missing value and an invalid value as unavailable.

For example, this expression returns a fallback text when self.Name is unavailable:

if self.Name.oclIsUndefined() then
  'Name is unavailable'
else
  self.Name
endif

The conditional-expression form is described in Documentation:OCLOperators if.

Null, invalid, and undefined

Value state	oclIsUndefined()	Meaning
null	true	The expression has no value.
invalid	true	The expression is invalid.
A defined, valid value	false	The expression can be used as its value type permits.

Difference from oclIsInvalid()

oclIsUndefined() includes both null and invalid. Use oclIsInvalid() when you need to test only for invalid and must distinguish it from null.

See also

• Documentation:OCL Expressions
• Documentation:OclIsInvalid
• Documentation:OCLOperators if

What is invalid?

You can distinguish a missing value from an invalid result when writing OCL expressions that must handle each state differently.

null means that an expression has no value. invalid is a separate state that oclIsInvalid() tests for. Both states are undefined for the purpose of oclIsUndefined(), so that operation returns true for either state.

State	Test result	Use when
null	expression.oclIsUndefined() returns true; expression.oclIsInvalid() returns false.	The value is missing and you want to provide a fallback or handle an optional value.
invalid	expression.oclIsUndefined() returns true; expression.oclIsInvalid() returns true.	You must detect invalid separately from null.

Example: an expression that returns null

safeCast returns null when the object is not an instance of the target subtype. In this example, self.address.safeCast(USAddress) is null when self.address is not a USAddress:

if self.address.safeCast(USAddress).oclIsUndefined() then
  'No US address'
else
  self.address.safeCast(USAddress).state
endif

Choose the test that matches your rule

Use oclIsUndefined() when null and invalid require the same result. For example, use it before showing fallback text for an unavailable value.

Use oclIsInvalid() when your rule must identify invalid and treat null differently. For example, test oclIsInvalid() before a separate oclIsUndefined() check when your expression needs one outcome for invalid and another for a missing value.