Same here.
My ECAS says "your application January 26, 2015 when I checked it at first but It was changed to null after changing my address.
I don't know exactly NULL mean. No need to worry.
It has been in processing.
on ecas
1.We received your null on January 26, 2015.
2.We started processing your application on February 28, 2015.
3.Medical results have been received.
on cic
5th ITA: Mar, 20th
Madical done: Mar, 31th
application submited: April 2th
Medical passed: April, 24th
Background in progress: April, 24th
(Cook/ FST / score 899)