Switch Statement for blank values

Hi All;

I used the belwo switch statement 

=

Switch(
(Fields!new_totalhours.Value < 60 or isnothing(Fields!new_totalhoursValue.Value)), " Zero Hours",
(Fields!new_totalhours.Value  >60 and  Fields!new_totalhours.Value  <=299),"1 to 4 Hours",
(Fields!new_totalhours.Value  >= 300 and  Fields!new_totalhours.Value  <=539),"5 to 8 Hours",
(Fields!new_totalhours.Value  >= 540 and  Fields!new_totalhours.Value  <= 719),"9 to 11 Hours",
(Fields!new_totalhours.Value  = 720),"12 Hours",
(Fields!new_totalhours.Value  > 720),"More than 12 Hours"
)

but this displays the blank value for 

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i need to add/combine  the blank and Zero Hours column together.

I need use the below statement but it didnt worked

isnothing(Fields!new_totalhoursValue.Value)

Any help much appreciated

Thanks

Pradnya07