ParamConverters code style & provider order fix.

- ex.getTargetException() -> ex.getCause()
- String.length() == 0 -> String.isEmpty()
- Date and JAXB providers put ahead of StringConstructor parameter provider.

Change-Id: Ic84aec77516eceb94efde3d7a0d542f2d8208642
Signed-off-by: Marek Potociar <marek.potociar@oracle.com>