You currently have your multivalue as the third parameter on your tool dialog but you are trying to reference it using an index value of 1:

multival = arcpy.GetParameterAsText(1)

when it should be referenced using an index value of 2:

multival = arcpy.GetParameterAsText(2)

You currently have your multivalue as the third parameter on your tool dialog but you are trying to reference it using an index value of 1:

multival = arcpy.GetParameterAsText(1)

when it should be referenced using an index value of 2:

multival = arcpy.GetParameterAsText(2)

Alternatively, you could leave the parameter index numbers as they are and use the up/down arrows on the Parameters tab of the tools Properties to move the parameter order on the tool dialog to match that of your code.