Allow multiple values issue on SSRS

Question

I would like to select multiple values parameter on SSRS. I used depended dropdown parameter. For example my type parameter data set is:

    select '<All>' 'TYPE'
union
    SELECT DISTINCT STR_TYPE   'TYPE'
        FROM [DBO].[MMWLOTS] L
        JOIN  [DBO].[MMWLOTPRPVALS]  P
    ON P.LOTPK=L.LOTPK
        JOIN [DBO].[LFP_MATERIALS] M
    ON M.STR_MATERIAL_ID=L.DEFID 

my class parameter's dataset code is: (class parameter dropdown list depends on type parameter value)

    select '<All>' 'CLASS'
union
    SELECT DISTINCT STR_CLASS 'CLASS'
    FROM [DBO].[MMWLOTS] L
        JOIN  [DBO].[MMWLOTPRPVALS]  P
    ON P.LOTPK=L.LOTPK
        JOIN [DBO].[LFP_MATERIALS] M
    ON M.STR_MATERIAL_ID=L.DEFID 
    WHERE (@MATERIAL_TYPE= '<All>' OR  M.STR_TYPE in (@MATERIAL_TYPE))

Normally I can show my report like this:

When I select the "allow multiple values" for class parameter and If I select two values for class, I face to below error:

How should I pass this error? Could you help me about this issue?

Thanks:)