In common usage, "none" is treated like a singular noun when the sentence is trying to attribute the absence of a property to each member of a group individually: "None of the dishes is going to be ready in time for dinner." When "none" is intended to attribute the absence of a property to an entire group collectively, so the reasoning goes, then it is treated like a plural noun: "None of my dishes require baking soda."
The belief that "none" can serve as a singular noun apparently comes from the incorrect assumption that it is a contraction of "not one," as I found out in
an interesting article. However, the article doesn't say quite say that "none" is
never a singular noun; it says only that it's not wrong to use it as a plural. It seems to be one of those cases where common usage has deemed it okay to use both.