DATAJPA-1549 - Indicate that "Is" in "IsNull" is optional.

Original pull request: spring-projects#238.

Author: ugultopu

src/main/asciidoc/jpa.adoc

@@ -198,7 +198,7 @@ The following table describes the keywords supported for JPA and what a method c
 |`GreaterThanEqual`|`findByAgeGreaterThanEqual`|`… where x.age >= ?1`
 |`After`|`findByStartDateAfter`|`… where x.startDate > ?1`
 |`Before`|`findByStartDateBefore`|`… where x.startDate < ?1`
-|`IsNull`|`findByAgeIsNull`|`… where x.age is null`
+|`IsNull`|`findByAge(Is)Null`|`… where x.age is null`
 |`IsNotNull,NotNull`|`findByAge(Is)NotNull`|`… where x.age not null`
 |`Like`|`findByFirstnameLike`|`… where x.firstname like ?1`
 |`NotLike`|`findByFirstnameNotLike`|`… where x.firstname not like ?1`