fix(influxdb): check if fields are empty before sending
Related Issue: https://emqx.atlassian.net/browse/EMQX-8461
Currently, the InfluxDB client raises an error if an empty `fields`
map is passed to it for pushing data.
```
14:03:35.563 [error] [InfluxDB] Encode [
%{
fields: %{},
measurement: "t/topic",
tags: %{},
timestamp: 1670864615563
}
] failed: :error :missing_field [
{:influxdb_line, :encode_fields, 1,
[
file: '/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl',
line: 60
]},
{:influxdb_line, :encode_, 1,
[
file: '/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl',
line: 44
]},
{:influxdb_line, :"-encode_/1-fun-0-", 2,
[
file: '/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl',
line: 38
]},
{:influxdb, :write, 2,
[file: '/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb.erl', line: 79]},
{:emqx_ee_connector_influxdb, :do_query, 3,
[
file: '/home/thales/dev/emqx/emqx/lib-ee/emqx_ee_connector/src/emqx_ee_connector_influxdb.erl',
line: 322
]},
{:emqx_resource_worker, :apply_query_fun, 6,
[
file: '/home/thales/dev/emqx/emqx/apps/emqx_resource/src/emqx_resource_worker.erl',
line: 454
]},
{:emqx_resource_worker, :query_or_acc, 3,
[
file: '/home/thales/dev/emqx/emqx/apps/emqx_resource/src/emqx_resource_worker.erl',
line: 306
]},
{:gen_statem, :loop_state_callback, 11, [file: 'gen_statem.erl', line: 1203]},
{:proc_lib, :init_p_do_apply, 3, [file: 'proc_lib.erl', line: 226]}
]
2022-12-12T14:03:35.563607-03:00 [error] [InfluxDB] Encode [#{fields => #{},measurement => <<"t/topic">>,tags => #{},timestamp => 1670864615563}] failed: error missing_field [{influxdb_line,encode_fields,1,[{file,"/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl"},{line,60}]},{influxdb_line,encode_,1,[{file,"/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl"},{line,44}]},{influxdb_line,'-encode_/1-fun-0-',2,[{file,"/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb_line.erl"},{line,38}]},{influxdb,write,2,[{file,"/home/thales/dev/emqx/emqx/deps/influxdb/src/influxdb.erl"},{line,79}]},{emqx_ee_connector_influxdb,do_query,3,[{file,"/home/thales/dev/emqx/emqx/lib-ee/emqx_ee_connector/src/emqx_ee_connector_influxdb.erl"},{line,322}]},{emqx_resource_worker,apply_query_fun,6,[{file,"/home/thales/dev/emqx/emqx/apps/emqx_resource/src/emqx_resource_worker.erl"},{line,454}]},{emqx_resource_worker,query_or_acc,3,[{file,"/home/thales/dev/emqx/emqx/apps/emqx_resource/src/emqx_resource_worker.erl"},{line,306}]},{gen_statem,loop_state_callback,11,[{file,"gen_statem.erl"},{line,1203}]},{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,226}]}]
14:03:35.565 [error] [connector: "bridge:influxdb_api_v2:aaa", msg: 'influxdb write point failed', reason: :missing_field]
2022-12-12T14:03:35.565345-03:00 [error] connector: <<"bridge:influxdb_api_v2:aaa">>, line: 335, mfa: emqx_ee_connector_influxdb:do_query/3, msg: influxdb write point failed, reason: missing_field
[]
14:03:35.565 [error] [id: "bridge:influxdb_api_v2:aaa", msg: :send_error, reason: :missing_field]
iex(emqx@127.0.0.1)2> 2022-12-12T14:03:35.565913-03:00 [error] id: <<"bridge:influxdb_api_v2:aaa">>, line: 396, mfa: emqx_resource_worker:handle_query_result/4, msg: send_error, reason: missing_field
```
Instead of raising, we check if the interpolation resulted in an empty
map due to lack of context and just fail the push more gracefully.
Related to this, the original issue _appears_ to be related to a
frontend issue (to be confirmed and fixed separately), where the
it is not encoding the field types:
https://emqx.atlassian.net/browse/EMQX-8461?focusedCommentId=24805
c0b208dd9e