[fix] Avoid sending wifi clients if there isn't any

[stargieg]

Invalid data in "#/interfaces/3/wireless/clients", validator says:

{} is not of type 'array'

Checklist

• I have read the OpenWISP Contributing Guidelines.
• I have manually tested the changes proposed in this pull request.
• I have written new test cases for new code and/or updated existing tests for changes to existing code.
• I have updated the documentation.

[stargieg]

I'm working on an other fix for
This can Fix #101 and #102

Invalid data in "#/interfaces/4/wireless/clients/5/vht", validator says:

None is not of type 'boolean'

looks like this

diff --git a/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua b/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
index b38d548..12fdd7c 100644
--- a/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
+++ b/openwisp-monitoring/files/lib/openwisp-monitoring/wifi.lua
@@ -30,6 +30,9 @@ function wifi.parse_hostapd_clients(clients)
   local data = {}
   for mac, properties in pairs(clients) do
     properties.mac = mac
+    if properties.ht and properties.ht == "None" then properties.ht = false end
+    if properties.vht and properties.vht == "None" then properties.vht = false end
+    if properties.he and properties.he == "None" then properties.he = false end
     table.insert(data, properties)
   end
   if #data > 0 then return data end

WIP Testing

[stargieg]

The message in openwisp2.log:

[INFO 2025-02-07 13:56:57,767] module: views, process: 135817, thread: 139275812288320
Invalid data in "#/interfaces/3/wireless/clients/1/he", validator says:

None is not of type 'boolean'

[WARNING 2025-02-07 13:56:57,768] module: log, process: 135817, thread: 139275812288320
Bad Request: /api/v1/monitoring/device/d94***569/

correlate with logread message:

host: 'ap7.***.net'
d94***569
Fri Feb  7 13:56:57 2025 daemon.err openwisp-monitoring[9358]: cat: can't open '/tmp/openwisp/monitoring/07-02-2025_12:56:57': No such file or directory

and come from:

openwrt-openwisp-monitoring/openwisp-monitoring/files/monitoring.agent

Line 153 in 8856b24

data=$(cat "$filename")

WIP