Influxdb: error when no data returned

[rozetko]

Currently you get error when no data for given range is returned in InfluxdbMetric

Guess it would be better to do like in GraphiteMetric:

if(res.data !== undefined && res.data.length < 1) {
  console.log('datasource return empty response, no data');
  return {
    columns: ['timestamp', 'target'],
    values: []
  };
}

@amper43 @jonyrock what do you think? Should we handle it? Maybe it should be handled by lib user?

[jonyrock]

@rozetko I don`t like how it is made in prometheus.

if(res.data === undefined) {
  throw new Error('undefined error');
}

and then continue

Please think for a second, what you gonna do if res.data IS undefined?