Gauge without label should not have a default value of 0 (zero)

[thomaschaaf]

A gauge that is registered but does not have a value set is currently set to 0 (zero). I believe this behavior to be incorrect because a gauge without a label does not work like it.

const client = require('prom-client');
const gauge = new client.Gauge({ name: 'metric_name', help: 'metric_help', labelNames: ['example'] });
const gauge2 = new client.Gauge({ name: 'metric_name2', help: 'metric_help2' });

console.log(await client.register.metrics())

gauge.set({ example: 'true' }, 1)

console.log(await client.register.metrics())

gauge.reset();

console.log(await client.register.metrics())

Output 1 after initialization:

# HELP metric_name metric_help
# TYPE metric_name gauge

# HELP metric_name2 metric_help2
# TYPE metric_name2 gauge
metric_name2 0

Output 2 after setting gauge:

# HELP metric_name metric_help
# TYPE metric_name gauge
metric_name{example="true"} 1

# HELP metric_name2 metric_help2
# TYPE metric_name2 gauge
metric_name2 0

Output 3 after reset:

# HELP metric_name metric_help
# TYPE metric_name gauge

# HELP metric_name2 metric_help2
# TYPE metric_name2 gauge
metric_name2 0

I would expect the output 1 of both gauges to be the same and instead of a default of 0 having a default of undefined.