SqlRowSet accessor methods should be marked @Nullable

[turbanoff]

We use org.springframework.jdbc.support.rowset.SqlRowSet in our project to extract data from PostgreSQL.
Recently I found out that IntelliJ IDEA shows warning where it shouldn't be.

As I understand it's because IDEA thinks that SqlRowSet.getString always return non-null value. But it's not true. It's because of @NonNullApi annotation in https://github.com/spring-projects/spring-framework/blob/master/spring-jdbc/src/main/java/org/springframework/jdbc/support/rowset/package-info.java

Need to mark all SqlRowSets methods which can return null as @Nullable to avoid static analyzer false-positive warnings.

[sbrannen]

Good catch.

@turbanoff, would you like to submit a PR to address this?

[jhoeller]

Actually, let me take this opportunity to generally revisit our use of the JDBC API which unfortunately comes with "unclean" nullability, so the static analyzers don't perform strict validation against it. Otherwise we would have discovered the mismatch in ResultSetWrappingSqlRowSet right away.

So from that perspective, no need for a PR... I can take this from here and backport it to 5.1.x and 5.0.x as well.