Exception: Unable to parse number with data: 0%

[Kahoulam]

Steps to reproduce

1. Create a new project
2. Add tokens.json file
3. Execute the command dart run build_runner build

Expected results

Correctly generate tokens.dart file

Actual results

An error occurred:

Exception: Unable to parse number with data: 0%

Version

design_tokens_builder: ^0.2.0+1

Code sample

tokens.json

{
  "global": {
    "letterSpacing": {
      "0": {
        "value": "-0.25",
        "type": "letterSpacing"
      },
      "1": {
        "value": "0%",
        "type": "letterSpacing"
      },
      "2": {
        "value": "0.15",
        "type": "letterSpacing"
      },
      "3": {
        "value": "0.1",
        "type": "letterSpacing"
      },
      "4": {
        "value": "0.5",
        "type": "letterSpacing"
      },
      "5": {
        "value": "0.25",
        "type": "letterSpacing"
      }
    }
  },
  "$themes": [],
  "$metadata": {
    "tokenSetOrder": [
      "global"
    ]
  }
}

Logs

Console logs

[INFO] Generating build script completed, took 240ms
[INFO] Reading cached asset graph completed, took 66ms
[INFO] Checking for updates since last build completed, took 846ms
[WARNING] design_tokens_builder|lib/design_tokens_builder.dart was not found in the asset graph, incremental builds will not work.
 This probably means you don't have your dependencies specified fully in your pubspec.yaml.
[WARNING] Invalidating asset graph due to build script update!
[INFO] Cleaning up outputs from previous builds. completed, took 1ms
[INFO] Generating build script completed, took 42ms
[WARNING] Invalidated precompiled build script due to missing asset graph.
[INFO] Precompiling build script... completed, took 607ms
[WARNING] design_tokens_builder|lib/design_tokens_builder.dart was not found in the asset graph, incremental builds will not work.
 This probably means you don't have your dependencies specified fully in your pubspec.yaml.
[INFO] Building new asset graph completed, took 924ms
[INFO] Checking for unexpected pre-existing outputs. completed, took 0ms
[SEVERE] design_tokens_builder on lib/$lib$:

Exception: Unable to parse number with data: 0%
[INFO] Running build completed, took 40ms
[INFO] Caching finalized dependency graph completed, took 42ms
[SEVERE] Failed after 88ms

Flutter Doctor output

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