panic: assignment to entry in nil map

[karimtabet]

We are seeing panic: assignment to entry in nil map when running ./postgresql-prometheus-adapter for the first time. The offending line appears to be this:

vMetricIDMap[sMetric] = nextId

Are we initialising vMetricIDMap properly?

$ ./postgresql-prometheus-adapter
ts=2022-10-28T16:42:45.954Z caller=main.go:129 level=info config="&{remoteTimeout:30000000000 listenAddr::9201 telemetryPath:/metrics pgPrometheusConfig:{CommitSecs:15 CommitRows:20000 PGWriters:1 PGParsers:5 PartitionScheme:hourly} logLevel: haGroupLockId:0 prometheusTimeout:0 promlogConfig:{Level:0xc000013470 Format:0xc000036650}}"
ts=2022-10-28T16:42:45.954Z caller=main.go:130 level=info pgPrometheusConfig="{CommitSecs:15 CommitRows:20000 PGWriters:1 PGParsers:5 PartitionScheme:hourly}"
ts=2022-10-28T16:42:45.968Z caller=main.go:172 level=info msg="Starting HTTP Listerner"
ts=2022-10-28T16:42:45.968Z caller=main.go:177 level=info msg="Starting up..."
ts=2022-10-28T16:42:45.968Z caller=main.go:178 level=info msg=Listening addr=:9201
ts=2022-10-28T16:42:45.989Z caller=client.go:241 level=info msg="creating tables"
ts=2022-10-28T16:42:45.991Z caller=client.go:314 level=info msg="Creating partition, hourly"
ts=2022-10-28T16:42:45.992Z caller=client.go:135 level=info bgwriter0="Starting 5 Parsers"
ts=2022-10-28T16:42:45.992Z caller=client.go:140 level=info bgwriter0=Started
ts=2022-10-28T16:42:45.992Z caller=client.go:69 level=info bgparser4=Started
ts=2022-10-28T16:42:45.992Z caller=client.go:69 level=info bgparser2=Started
ts=2022-10-28T16:42:45.992Z caller=client.go:69 level=info bgparser3=Started
ts=2022-10-28T16:42:45.992Z caller=client.go:69 level=info bgparser0=Started
ts=2022-10-28T16:42:45.992Z caller=client.go:69 level=info bgparser1=Started
ts=2022-10-28T16:42:47.361Z caller=client.go:314 level=info msg="Creating partition, hourly"
ts=2022-10-28T16:42:47.363Z caller=client.go:314 level=info msg="Creating partition, hourly"
panic: assignment to entry in nil map

goroutine 24 [running]:
github.com/crunchydata/postgresql-prometheus-adapter/pkg/postgresql.(*PGParser).RunPGParser(0xc000199900, 0x4e20?, {0xb20fc1, 0x6}, 0x1055ae0)
	/root/postgresql-prometheus-adapter/pkg/postgresql/client.go:92 +0x67e
created by github.com/crunchydata/postgresql-prometheus-adapter/pkg/postgresql.(*PGWriter).RunPGWriter
	/root/postgresql-prometheus-adapter/pkg/postgresql/client.go:137 +0x545