Sending multiple links to a *-to-one association responds with 500 Internal Server Error

[NielsCW]

When sending multiple links to a one-to-one or many-to-one association, the server responds with 500 Internal server error due to the RepositoryPropertyReferenceController throwing an IllegalArgumentException (message: "Must send only 1 link to update a property reference that isn't a List or a Map."). Since a general IllegalArgumentException is thrown, this results in a HTTP 500 error from

spring-data-rest/spring-data-rest-webmvc/src/main/java/org/springframework/data/rest/webmvc/RepositoryRestExceptionHandler.java

Lines 88 to 99 in aaadc34

	/**
	* Handle failures commonly thrown from code tries to read incoming data and convert or cast it to the right type by
	* returning {@code 500 Internal Server Error} and the thrown exception marshalled into JSON.
	*
	* @param o_O the exception to handle.
	* @return
	*/
	@ExceptionHandler({ InvocationTargetException.class, IllegalArgumentException.class, ClassCastException.class,
	ConversionFailedException.class, NullPointerException.class })
	ResponseEntity<ExceptionMessage> handleMiscFailures(Exception o_O) {
	return errorResponse(HttpStatus.INTERNAL_SERVER_ERROR, new HttpHeaders(), o_O);

.
Typically, the response for an error triggered by user input would be in the 4xx range, e.g. 400 Bad Request.
If a more specific exception was thrown, it could be handled by the ExceptionHandler to return a more correct HTTP error, and developers that integrate spring-data-rest can supply their own @ExceptionHandler to handle this error as well.