Variable '<variablename>' is passed by reference before it has been assigned a value
Variable '<variablename>' is passed by reference before it has been assigned a value. A null reference exception could result at run time.
A procedure call passes a variable as an argument to a ByRef parameter before any value is assigned to the variable.
If a variable has never been assigned a value, it holds the default value for its data type. For a reference data type, that default value is Nothing (Visual Basic). Reading a reference variable that has a value of Nothing can cause a NullReferenceException in some circumstances.
Passing an argument to a procedure ByRef exposes the variable underlying the argument to possible modification by the procedure.
By default, this message is a warning. For more information about hiding warnings or treating warnings as errors, see Configuring Warnings in Visual Basic.
Error ID: BC42030
To correct this error
If you intend the procedure to assign a value to the variable through the ByRef argument, and if it does not matter whether the variable already holds a value, then no action is necessary.
If the logic in the procedure reads the argument before assigning any value to it, and if the variable is of a value type, then make sure that the procedure logic does not depend on whether the variable holds its default value or not.
If the logic in the procedure reads the argument before assigning any value to it, and if the variable is of a reference type, then make sure that the procedure logic can handle a value of Nothing. For example, it could use a Try...Catch...Finally Statement (Visual Basic) to catch a NullReferenceException.
See Also
Tasks
Troubleshooting Variables in Visual Basic
Concepts
Value Types and Reference Types
Passing Arguments by Value and by Reference
Variable Declaration in Visual Basic