[BUG] Can't delete location file

[fbielejec]

Problem

Can't delete locations file in Discrete analysis (both tree and rates):

{"errors":[{"message":"No value was provided for variable `url', which is non-nullable.","locations":[{"line":2,"column":36}],"extensions":{"field-name":"Mutation/deleteFile","argument":"Mutation/deleteFile.url","variable-name":"url"}}]}