has been used with both singular and plural verbs since the 9th century. Source
It is widely asserted that none is equivalent to no one, and hence requires a singular verb and singular pronoun. The choice between a singular or plural verb depends on the desired effect. Both options are acceptable in this sentence:
None of the conspirators has (or have) been brought to trial.
When none is modified by almost, however, it is difficult to avoid treating the word as a plural:
Almost none of the officials were (not was) interviewed by the committee.
None can only be plural in its use in sentences such as None but his most loyal supporters believe (not believes) his story. Source
Some people insist that since “none” is derived from “no one” it should always be singular: “none of us is having dessert.” However, in standard usage, the word is most often treated as a plural. “None of us are having dessert” will do just fine. Source
One special problem occurs with the word none, which has its origin in the phrase not one. Because of that original meaning, many writers insist that none always be singular, as not one clearly is. However, a more accurate way to assess its meaning is to recognize none as the negative, or opposite, of all and to treat it in the same way, with its number determined by the number of the modifier. Examples
All of the cake was
None of the cake was
All of the cookies were
None of the cookies were
~Martha Kolln, Rhetorical Grammar Source
It’s uncertain who started the notion that none requires a singular verb, but it’s pervasive, both in the US and Britain, and seems to have been drummed into the heads of generations of schoolchildren. However, all the usage guides — and the usage notes in every dictionary that I can find — are unanimous in saying that it’s wrong.
The argument stems from a misunderstanding of where the word comes from. People assume that none is a condensed form of no one or not one.
Read more here: World Wide Words: Singular or plural verb with 'none'
If you were taught that the word none is always singular, you were taught a half-truth. Yes, none can be singular, but it can be plural as well. Respected writers have been using the word both ways for a very long time.
Those who once argued that none must be singular claimed that it meant “not a single one.” In fact, though, it quite often means “not any.” Writers are more or less free to decide which meaning is appropriate in their context. Advice given by Richard Lederer and Richard Dowis is typical: “Consider none as singular when you want to emphasize a single entity in a group. Consider it plural when you want to emphasize more than one” (98). For Lederer and Dowis, both of these sentences are acceptable:
None of us is going to the party.
None of us are going to the party. Source