fix byte[] null bug

xueyi-common/xueyi-common-core/src/main/java/com/xueyi/common/core/utils/DecodeRequestUtils.java

@@ -23,6 +23,9 @@ public class DecodeRequestUtils {
 	 */
 	public static String getRequestPostStr(HttpServletRequest request) throws IOException {
 		byte[] buffer = getRequestPostBytes(request);
+		if  (buffer == null) {
+			return "";
+		}
 		String charEncoding = request.getCharacterEncoding();
 		if (charEncoding == null) {
 			charEncoding = "UTF-8";