iluwatar#355 handle case when there are no child elements for the given key

Author: qza

abstract-document/src/main/java/com/iluwatar/abstractdocument/AbstractDocument.java

@@ -3,6 +3,7 @@
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Optional;
 import java.util.function.Function;
 import java.util.stream.Stream;
 
@@ -28,11 +29,11 @@ public Object get(String key) {
 
     @Override
     public <T> Stream<T> children(String key, Function<Map<String, Object>, T> constructor) {
-        return Stream.of(get(key))
+        Optional<List<Map<String, Object>>> any = Stream.of(get(key))
                 .filter(el -> el != null)
                 .map(el -> (List<Map<String, Object>>) el)
-                .findAny().get().stream()
-                .map(constructor);
+                .findAny();
+        return any.isPresent() ? any.get().stream().map(constructor) : Stream.empty();
     }
 
     @Override

abstract-document/src/test/java/com/iluwatar/abstractdocument/AbstractDocumentTest.java

@@ -29,7 +29,6 @@ private class DocumentImplementation extends AbstractDocument {
     public void shouldPutAndGetValue() {
         document.put(KEY, VALUE);
         assertEquals(VALUE, document.get(KEY));
-        System.out.println(document);
     }
 
     @Test
@@ -45,4 +44,11 @@ public void shouldRetrieveChildren() {
         assertEquals(2, childrenStream.count());
     }
 
+    @Test
+    public void shouldRetrieveEmptyStreamForNonExistinChildren() {
+        Stream<DocumentImplementation> children = document.children(KEY, DocumentImplementation::new);
+        assertNotNull(children);
+        assertEquals(0, children.count());
+    }
+
 }