Polishing.

Fix Javadoc.

See #1872
Original pull request: #1874

spring-data-jdbc/src/main/java/org/springframework/data/jdbc/repository/query/AbstractJdbcQuery.java

@@ -76,7 +76,7 @@ public JdbcQueryMethod getQueryMethod() {
 	 * Creates a {@link JdbcQueryExecution} given a {@link ResultSetExtractor} or a {@link RowMapper}. Prefers the given
 	 * {@link ResultSetExtractor} over {@link RowMapper}.
 	 *
-	 * @param extractor must not be {@literal null}.
+	 * @param extractor may be {@literal null}.
 	 * @param rowMapper must not be {@literal null}.
 	 * @return a JdbcQueryExecution appropriate for {@literal queryMethod}. Guaranteed to be not {@literal null}.
 	 */