Fix NPE in `CrudRepositoryExtensions`.

Closes #3187

src/main/kotlin/org/springframework/data/repository/CrudRepositoryExtensions.kt

@@ -19,8 +19,9 @@ package org.springframework.data.repository
  * Retrieves an entity by its id.
  *
  * @param id the entity id.
- * @return the entity with the given id or `null` if none found
+ * @return the entity with the given id or `null` if none found.
  * @author Sebastien Deleuze
+ * @author Oscar Hernandez
  * @since 2.1.4
  */
-fun <T, ID> CrudRepository<T, ID>.findByIdOrNull(id: ID): T? = findById(id!!).orElse(null)
+fun <T, ID: Any> CrudRepository<T, ID>.findByIdOrNull(id: ID): T? = findById(id).orElse(null)