JSON response outputs `"NULL"` instead of `null` when `formatter: 1`

[Raruto]

Checklist

• [X] I've searched through the existing issues and this bug has never been reported before

Subject of the issue

Null values are converted to string when sent to HTTP response (formatter: 1) causing an inconsistent handling in JS code:

Steps to reproduce

"formatter": 1

// outputs: "NULL"

fetch('https://v37.g3wsuite.it/vector/api/data/qdjango/97/buildings_2f43dc1d_6725_42d2_a09b_dd446220104a/', {
  method: 'POST',
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "field": "type|eq|Administrative",
    "formatter": 1,
  }),
}).then(d => d.json()).then(d => console.log(d.vector.data.features[4].properties.subtype))

"formatter": 0

// outputs: null

fetch('https://v37.g3wsuite.it/vector/api/data/qdjango/97/buildings_2f43dc1d_6725_42d2_a09b_dd446220104a/', {
  method: 'POST',
  headers: { "Content-Type": "application/json" },
  body: JSON.stringify({
    "field": "type|eq|Administrative",
    "formatter": 0,
  }),
}).then(d => d.json()).then(d => console.log(d.vector.data.features[4].properties.subtype))

Environment

[g3wsdk.info]

• g3w-admin: v3.7.6
• g3w-client: 3.9.5
• browser: Firefox 124.0
• operating system: Windows 10 64-bit

Link to your project

https://v37.g3wsuite.it/en/map/demo-37/

Additional info

No response