customAction fetch request handling

[akelch]

Description

Frontend error handling fails when the response object is undefined.

Additionally, the current handling appears to call .json() without validating whether the response actually contains application/json.

Expected Behavior

• Undefined response objects are handled safely.
• .json() is only called for JSON responses.
• Non-JSON responses are handled via .text() or another suitable fallback.
• The original error should remain visible and understandable.

Observed Behavior

The frontend throws:

Uncaught (in promise) TypeError: Cannot read properties of undefined (reading 'json')
    at index-*.js:4232:86238

This indicates that .json() is called on an undefined value.

There also appears to be no content-type check before parsing the response as JSON.

Technical Notes

Current behavior likely assumes a valid JSON response object:

response.json()

Safer handling should validate both the response and the content type:

if (!response) {
  throw new Error("No response object available");
}

const contentType = response.headers?.get("content-type") || "";

const payload = contentType.includes("application/json")
  ? await response.json()
  : await response.text();

Acceptance Criteria

• No .json() call is made on an undefined response.
• JSON parsing only happens for responses with JSON content type.
• Non-JSON responses are handled without throwing parser-related errors.
• The original request or backend error remains debuggable.