Foundry376/Mailspring · error · Error

Validation failed at ${keyPath}, ${JSON.stringify(value)} mu

Error message

Validation failed at ${keyPath}, ${JSON.stringify(value)} must be a string

What it means

Config schema enforcer for type 'string' (validate pass, no coercion): the value stored or being set at keyPath has a non-string type. The string enforcer deliberately does not stringify numbers/objects, so callers must pass actual strings.

Source

Thrown at app/src/config.ts:817

              )} must be a boolean or the string 'true' or 'false'`
            );
          }
        case 'boolean':
          return value;
        default:
          throw new Error(
            `Validation failed at ${keyPath}, ${JSON.stringify(
              value
            )} must be a boolean or the string 'true' or 'false'`
          );
      }
    },
  },

  string: {
    validate(keyPath, value, schema) {
      if (typeof value !== 'string') {
        throw new Error(
          `Validation failed at ${keyPath}, ${JSON.stringify(value)} must be a string`
        );
      }
      return value;
    },
  },

  null: {
    // null sort of isnt supported. It will just unset in this case
    coerce(keyPath, value, schema) {
      if (![undefined, null].includes(value)) {
        throw new Error(`Validation failed at ${keyPath}, ${JSON.stringify(value)} must be null`);
      }
      return value;
    },
  },

  object: {

View on GitHub (pinned to 648c685d60)

Solutions

1. Convert the value to a string before setting (String(value) or template literal)
2. Fix hand-edited JSON where a string setting was written as a number/boolean

When it happens

Trigger: Thrown at app/src/config.ts:817 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of Foundry376/Mailspring@648c685d60 (2026-09-03). Data as JSON: /api/errors/00b0a380be7c7834. Report an issue: GitHub.