RDC00207 — IsMissing that is always False

Severity: Warning · Family: RDC (Rubberduck Core analyzers) · Raised by: IsMissingAlwaysFalseAnalyzer

IsMissing is given a parameter that can never be missing, so it always returns False.

IsMissing tells whether an Optional argument was left out of a call (MS-VBAL §6.1.2.7.1.6). It can only tell for a Variant parameter: an argument left out of a call leaves a parameter of any other type the default value of its type - 0, an empty string, Nothing - which is a value like any other, and gives an Optional Variant its default value when it has one. Code that tests IsMissing of such a parameter looks like it handles the argument being left out, and never does. MS-VBA compiles it without a word.

A Variant parameter with no default value can be missing, whether it is Optional or not (an argument that was left out, passed on to it), and so can a ParamArray that was given no arguments: neither is reported. The fact is the environment host's, from the declaration of the parameter (ValueExpressionSemanticFlags.IsMissingAlwaysFalse).

How it is raised

Situation	Example	Resolution
The parameter is not a `Variant`.	`Sub Report(Optional Copies As Long)` … `If IsMissing(Copies) Then`	Give it a default value and test for that (`Optional Copies As Long = 1`), or declare it `As Variant`.
The parameter is an `Optional` `Variant` with a default value.	`Sub Report(Optional Title As Variant = "")` … `If IsMissing(Title) Then`	Test for the default value, or remove it so that `IsMissing` can tell.

The results are MS-VBA's, recorded in Excel: IsMissing of an Optional n As Long, an Optional s As String, an Optional o As Object and an Optional v As Variant = 5 is False when the argument is left out; of an Optional v As Variant, and of a ParamArray given nothing, it is True.

Table of Contents

RDC00207 — IsMissing that is always False

How it is raised

See also