throw exceptions at most relevant place with relevant description

[GoogleCodeExporter]

What steps will reproduce the problem?
   pass an empty string to a ofy().load().type(Foo.class).filter("bar =", emptyString)

What is the expected output? What do you see instead?
   Exception should state "Illegal argument to filter: value passed to be filtered against must not be null or empty",
   but it cryptically states "name must not me null or empty" at createkey

What version of the product are you using? On what operating system?
   4.0rc1

Please provide any additional information below.
   I'd catch this and throw at higher level

Original issue reported on code.google.com by jackp...@gmail.com on 15 Aug 2013 at 10:36

[GoogleCodeExporter]

Original comment by lhori...@gmail.com on 16 Aug 2013 at 2:09

• Changed state: Accepted