File mime type becomes content/unknown

I have this RESTful API where the Content-Type is multipart/form-data and I am attaching a JSON file in the form-data

Here is my function:
@ Keyword
def uploadAJsonFile (String fileName = “sample.json”) {
File file = new File("$exportDirPath/$fileName"’);
URLConnection connection = file.toURL().openConnection();
String mimeType = connection.getContentType();

	assert(mimeType == 'application/json');
            // Request.sendRequestRobust(findTestObject())

Even before passing the file into the RESTful API, the mimeType is already content/unknown which is not the expected mime

Caused by: Assertion failed: 

assert(mimeType == 'application/json')
                   |         |
                   |         false

The @Keyword mentioned above was working up until I upgraded to Katalon 7.4

Did anyone experienced the same thing? What did you do to get the correct mimeType for the file?

Thanks in advance!