Unable to transform positive number to negative when group_by func is delta

[davoau]

Checklist

• [✓] I updated the card to the latest version available
• [✓] I cleared the cache of my browser
• [✓] I verified that I'm really running the lastest version in my browser console
• [✓] I checked if there is another issue opened with the same problem

Desktop (please complete the following information):

• Browser: chrome
• Version: 132.0.6834.160 (Official Build) (64-bit)

Describe the bug
I can not change a positive number (float) to negative number using transform: -x; when group_by func: delta is used. This is for export to grid values from energy meter.

I can multiply and divide the number without issue, but can't subtract or add to it.

Version of the card
Version: 2.12

To Reproduce
This is the configuration I used:

type: custom:apexcharts-card
header:
  standard_format: false
  show: true
  show_states: true
  colorize_states: true
  title: Grid Import/Export
graph_span: 24h
show:
  last_updated: true
apex_config:
  chart:
    height: 395
    extend_to: now
  yaxis:
    show: true
    forceNiceScale: true
  stroke:
    show: true
    width: 1
  legend:
    show: true
stacked: true
series:
  - entity: sensor.energy_grid_import_hourly
    type: column
    name: Import
    float_precision: 2
    group_by:
      func: delta
      duration: 1h
  - entity: sensor.energy_grid_export_hourly
    type: column
    name: Export
    transform: return -x;
    float_precision: 2
    group_by:
      func: delta
      duration: 1h

Full code (configuration.yaml and apexchart card) can be found here:
https://community.home-assistant.io/t/apexcharts-card-a-highly-customizable-graph-card/272877/4183

This is what the resulting graph looks like with transform: return -x;, result (x * -1); produces a blank graph with LOADING displayed.

All other func options seem to work ok, except for diff.

[vingerha]

The same applies for func: diff
Added to that, when using delta grouping, transform: return 1 + x; the returned figures are more than odd
@RomRider if you have ideas on a direction, I am OK to spend time on it