can you add more comments here (and probably unit / regression test )? It's not immediately obvious what use case your change solves

Sorry about that. The use-case is for when one passes an options object to connection.query() with the intent to stream the results (i.e. no callback is passed). Previously options.values would be overridden to an undefined variable (the values argument) if no callback was set.

example (as demonstrated in the test file):

var query = connection.query({
  sql: 'SELECT ?',
  values: [ 'value' ]
});
query.on('err', ...)
query.on('result', ...)

thanks, makes sense now