Fix mapping empty page (#3180)

* Fix mapping empty page

* Just found wrong reference in docs and will push fix in this unrelated PR

data-model/src/main/java/io/micronaut/data/model/CursoredPage.java

@@ -52,7 +52,7 @@
 @DefaultImplementation(DefaultCursoredPage.class)
 public interface CursoredPage<T> extends Page<T> {
 
-    CursoredPage<?> EMPTY = new DefaultCursoredPage<>(Collections.emptyList(), Pageable.unpaged(), Collections.emptyList(), null);
+    CursoredPage<?> EMPTY = new DefaultCursoredPage<>(Collections.emptyList(), Pageable.unpaged(), Collections.emptyList(), -1L);
 
     /**
      * @return Whether this {@link CursoredPage} contains the total count of the records
@@ -125,6 +125,9 @@ default CursoredPageable previousPageable() {
      */
     @Override
     default @NonNull <T2> CursoredPage<T2> map(Function<T, T2> function) {
+        if (this == EMPTY) {
+            return (CursoredPage<T2>) EMPTY;
+        }
         List<T2> content = getContent().stream().map(function).collect(Collectors.toList());
         return new DefaultCursoredPage<>(content, getPageable(), getCursors(), hasTotalSize() ? getTotalSize() : null);
     }

data-model/src/main/java/io/micronaut/data/model/Page.java

@@ -96,6 +96,9 @@ default boolean hasNext() {
      */
     @Override
     default @NonNull <T2> Page<T2> map(Function<T, T2> function) {
+        if (this == EMPTY) {
+            return (Page<T2>) EMPTY;
+        }
         List<T2> content = getContent().stream().map(function).toList();
         return new DefaultPage<>(content, getPageable(), hasTotalSize() ? getTotalSize() : null);
     }

data-model/src/test/groovy/io/micronaut/data/model/PageSpec.groovy

@@ -199,6 +199,24 @@ class PageSpec extends Specification {
         !mappedCursoredPage.hasTotalSize()
     }
 
+    void "empty page can be mapped "() {
+        when:
+        Page<String> page = Page.empty()
+        def copy = page.map { it -> it }
+        copy.getTotalSize()
+
+        then:
+        notThrown(Throwable)
+
+        when:
+        CursoredPage<String> cursoredPage = CursoredPage.empty()
+        def newCopy = cursoredPage.map {it -> it }
+        newCopy.getTotalSize()
+
+        then:
+        notThrown(Throwable)
+    }
+
     @EqualsAndHashCode
     @ToString
     @Serdeable

src/main/docs/guide/azureCosmos/azureCosmosCriteriaSpecifications.adoc

@@ -4,7 +4,7 @@ dependency:jakarta.persistence:jakarta.persistence-api[]
 
 To implement queries that cannot be defined at the compile-time Micronaut Data introduces api:data.repository.JpaSpecificationExecutor[] repository interface that can be used to extend your repository interface:
 
-snippet::example.PersonRepository[project-base="doc-examples/mongo-example",source="main" tags="repository",indent="0"]
+snippet::example.PersonRepository[project-base="doc-examples/azure-cosmos-example",source="main" tags="repository",indent="0"]
 
 Each method expects a "specification" which is a functional interface with a set of Criteria API objects intended to build a query programmatically.