JERSEY-1577: WebTarget throws IAE instead of NPE

  - fix + test

Change-Id: I66294b62c2f5d3f597a136b8111536e636e24780
JERSEY-1511: MessageBodyReader does not set default content-type

 - fix + test

Change-Id: I4e584ced6c68d134216acfa080e017d9e1081970
Merge "JERSEY-1577: WebTarget throws IAE instead of NPE"
Merge "JERSEY-1511: MessageBodyReader does not set default content-type"