POST/PUT request to packages/resources with invalid "customCoverage" gives 400 with stack trace

When we make a POST to /eholdings/packages with the following request body, we get a 400 but with a stacktrace instead of an error response.

{
	"data": {
		"type": "packages",
		"attributes": {
			"name": "123",
			"contentType": "ejournal",
			"customCoverage": {
				"beginCoverage": 2003-01-01, 
				"endCoverage": 2003-12-01
			}
		}
	}
}

The issue with the above is that "beginCoverage" and "endCoverage" are not strings as expected by code.