GH-1542: Fix regression about creating attributes with null value.

leshan-core/src/main/java/org/eclipse/leshan/core/link/attributes/AttributeModel.java

@@ -22,7 +22,7 @@
  */
 public abstract class AttributeModel<T extends Attribute> {
 
-    private String name;
+    private final String name;
 
     public AttributeModel(String name) {
         this.name = name;
@@ -55,4 +55,9 @@ public T createEmptyAttribute() throws UnsupportedOperationException {
     public boolean linkAttributeCanBeValueless() {
         return false;
     }
+
+    @Override
+    public String toString() {
+        return getName();
+    }
 }

leshan-core/src/main/java/org/eclipse/leshan/core/link/lwm2m/attributes/PositiveDoubleAttributeModel.java

@@ -31,7 +31,7 @@ public PositiveDoubleAttributeModel(String coRELinkParam, Attachment attachment,
 
     @Override
     public String getInvalidValueCause(Double value) {
-        if (value < 0) {
+        if (value != null && value < 0) {
             return String.format("'%s' attribute value must not be negative", getName());
         }
         return null;

leshan-core/src/main/java/org/eclipse/leshan/core/link/lwm2m/attributes/PositiveLongAttributeModel.java

@@ -31,7 +31,7 @@ public PositiveLongAttributeModel(String coRELinkParam, Attachment attachment,
 
     @Override
     public String getInvalidValueCause(Long value) {
-        if (value < 0) {
+        if (value != null && value < 0) {
             return String.format("'%s' attribute value must not be negative", getName());
         }
         return null;

leshan-core/src/test/java/org/eclipse/leshan/core/link/lwm2m/attributes/LwM2mAttributesTest.java

@@ -0,0 +1,77 @@
+/*******************************************************************************
+ * Copyright (c) 2023 Sierra Wireless and others.
+ *
+ * All rights reserved. This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * and Eclipse Distribution License v1.0 which accompany this distribution.
+ *
+ * The Eclipse Public License is available at
+ *    http://www.eclipse.org/legal/epl-v20.html
+ * and the Eclipse Distribution License is available at
+ *    http://www.eclipse.org/org/documents/edl-v10.html.
+ *
+ * Contributors:
+ *     Sierra Wireless - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.leshan.core.link.lwm2m.attributes;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+
+import org.eclipse.leshan.core.link.attributes.InvalidAttributeException;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class LwM2mAttributesTest {
+
+    private static Stream<Arguments> supportNullAttributes() throws InvalidAttributeException {
+        return Stream.of(//
+                Arguments.of(LwM2mAttributes.MINIMUM_PERIOD), //
+                Arguments.of(LwM2mAttributes.MAXIMUM_PERIOD), //
+                Arguments.of(LwM2mAttributes.EVALUATE_MINIMUM_PERIOD), //
+                Arguments.of(LwM2mAttributes.EVALUATE_MAXIMUM_PERIOD), //
+                Arguments.of(LwM2mAttributes.LESSER_THAN), //
+                Arguments.of(LwM2mAttributes.GREATER_THAN), //
+                Arguments.of(LwM2mAttributes.STEP) //
+        );
+    }
+
+    @ParameterizedTest(name = "Tests {index} : {0}")
+    @MethodSource("supportNullAttributes")
+    public void check_attribute_can_be_created_with_null_value(LwM2mAttributeModel<?> model)
+            throws InvalidAttributeException {
+        LwM2mAttribute<?> attribute = LwM2mAttributes.create(model);
+        assertNotNull(attribute);
+        assertFalse(attribute.hasValue());
+        assertNull(attribute.getValue());
+        attribute = LwM2mAttributes.create(model, null);
+        assertNotNull(attribute);
+        assertFalse(attribute.hasValue());
+        assertNull(attribute.getValue());
+    }
+
+    private static Stream<Arguments> doesntSupportNullAttributes() throws InvalidAttributeException {
+        return Stream.of(//
+                Arguments.of(LwM2mAttributes.DIMENSION), //
+                Arguments.of(LwM2mAttributes.ENABLER_VERSION), //
+                Arguments.of(LwM2mAttributes.OBJECT_VERSION), //
+                Arguments.of(LwM2mAttributes.SHORT_SERVER_ID), //
+                Arguments.of(LwM2mAttributes.SERVER_URI)//
+        );
+    }
+
+    @Disabled
+    @ParameterizedTest(name = "Tests {index} : {0}")
+    @MethodSource("doesntSupportNullAttributes")
+    // TODO implement this correctly : https://github.com/eclipse-leshan/leshan/issues/1542
+    public void check_attribute_can_not_be_created_with_null_value(LwM2mAttributeModel<?> model) {
+        assertThrows(InvalidAttributeException.class, () -> LwM2mAttributes.create(model));
+        assertThrows(InvalidAttributeException.class, () -> LwM2mAttributes.create(model, null));
+    }
+}