Fix AspectModelLoader throws NullPointerException by adding another message and exception type

Author: Yauhenikapl

core/esmf-aspect-meta-model-java/src/main/java/org/eclipse/esmf/aspectmodel/loader/Instantiator.java

@@ -116,7 +116,14 @@ protected Type getType( final Resource characteristicResource ) {
    private Statement getDataType( final Resource resource ) {
       return Optional.ofNullable( resource.getPropertyResourceValue( SammNs.SAMMC.baseCharacteristic() ) )
             .map( this::getDataType )
-            .orElseGet( () -> resource.getProperty( SammNs.SAMM.dataType() ) );
+            .orElseGet( () -> {
+               final Statement dataType = resource.getProperty( SammNs.SAMM.dataType() );
+               if ( dataType == null ) {
+                  throw new IllegalStateException(
+                        String.format( "No datatype is defined on the Characteristic instance '%s: '.", resource.getLocalName() ) );
+               }
+               return dataType;
+            } );
    }
 
    protected Optional<Characteristic> getElementCharacteristic( final Resource collection ) {

core/esmf-aspect-meta-model-java/src/test/java/org/eclipse/esmf/aspectmodel/loader/AspectModelLoaderTest.java

@@ -14,6 +14,7 @@
 package org.eclipse.esmf.aspectmodel.loader;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.AssertionsForClassTypes.assertThatThrownBy;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -40,6 +41,15 @@
 import org.junit.jupiter.api.Test;
 
 class AspectModelLoaderTest {
+
+   @Test
+   void loadAspectModelWithoutCharacteristicDatatype() {
+      assertThatThrownBy( () -> new AspectModelLoader().load( AspectModelLoaderTest.class.getResourceAsStream(
+            String.format( "/%s/invalid_characteristic_datatype.ttl", KnownVersion.SAMM_2_1_0 ) ) ) )
+            .isInstanceOf( IllegalStateException.class )
+            .hasMessage( "No datatype is defined on the Characteristic instance 'Characteristic1: '." );
+   }
+
    @Test
    void testOfAbstractEntityCyclomaticCreation() {
       final Map<String, ComplexType> entities =

core/esmf-aspect-meta-model-java/src/test/resources/samm_2_1_0/invalid_characteristic_datatype.ttl

@@ -0,0 +1,24 @@
+# Copyright (c) 2024 Robert Bosch Manufacturing Solutions GmbH
+#
+# See the AUTHORS file(s) distributed with this work for additional
+# information regarding authorship.
+#
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at https://mozilla.org/MPL/2.0/.
+#
+# SPDX-License-Identifier: MPL-2.0
+
+@prefix samm: <urn:samm:org.eclipse.esmf.samm:meta-model:2.1.0#> .
+@prefix samm-c: <urn:samm:org.eclipse.esmf.samm:characteristic:2.1.0#> .
+@prefix : <urn:samm:com.example.test:1.0.0#> .
+
+:AspectWithoutCharacteristicDatatype a samm:Aspect ;
+   samm:properties ( :property1 ) ;
+   samm:operations () ;
+   samm:events ( ) .
+
+:property1 a samm:Property ;
+   samm:characteristic :Characteristic1 .
+
+:Characteristic1 a samm:Characteristic .