This PR fixes a critical issue where the plugin would crash with Cannot set properties of undefined (setting 'installId') when the homebridge config file didn't have a properly initialized credentials object for the August platform.

Problem

The error occurred in the validated() method when trying to set properties on pluginConfig.credentials:

pluginConfig.credentials.installId = this.config.credentials?.installId

This happened because:

1. When credentials was completely missing from the config file, it would be undefined
2. When credentials was explicitly set to null, the existing check typeof pluginConfig.credentials !== 'object' would pass (since typeof null === 'object' in JavaScript), but then trying to set properties on null would fail

Solution

Updated the pluginConfig() method to properly handle both null and undefined credentials:

// Before: Only checked for non-object types
if (typeof pluginConfig.credentials !== 'object') {
  throw new TypeError('pluginConfig.credentials is not an object')
}

// After: Explicitly check for null and undefined, then initialize
if (typeof pluginConfig.credentials !== 'object' || pluginConfig.credentials === null) {
  pluginConfig.credentials = {}
}

Now when the validated() method runs, it can safely set properties on pluginConfig.credentials because the object is guaranteed to exist.

Testing

Added comprehensive tests to verify:

• Undefined credentials in config file are handled gracefully
• Null credentials in config file are handled gracefully
• The credentials object is properly initialized and the installId is saved

All existing tests continue to pass, ensuring no regressions.

Fixes #169.

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