feat: add nullable to model config params

service/definition/src/main/java/ai/timefold/solver/service/definition/internal/descriptor/ModelConfigParameter.java

@@ -18,6 +18,7 @@
  * @param arrayItemType the OpenAPI schema type for array items
  * @param format the data format which further specifies the schema type
  * @param schemaTypeRef the OpenAPI schema type reference (used when the schema type is not a primitive type)
+ * @param nullable whether the parameter accepts {@code null} as a value, as defined by the OpenAPI schema
  * @param constraintNameRef the constraint name reference (used when the parameter is a constraint weight or any other parameter
  *        related to a constraint)
  */
@@ -30,6 +31,7 @@ public record ModelConfigParameter(
         SchemaType arrayItemType,
         DataFormat format,
         String schemaTypeRef,
+        boolean nullable,
         String constraintNameRef) {
 
 }

service/quarkus/deployment/src/main/java/ai/timefold/solver/service/quarkus/deployment/TimefoldModelDescriptorProcessor.java

@@ -1439,6 +1439,7 @@ private ModelConfigParameter resolveModelConfigParameter(FieldInfo fieldInfo) {
         String description = null;
         SchemaType type = null;
         DataFormat format = null;
+        boolean nullable = false;
         Optional<AnnotationInstance> schemaAnnotationOptional = getSchemaAnnotation(fieldInfo);
         if (schemaAnnotationOptional.isPresent()) {
             AnnotationInstance schemaAnnotation = schemaAnnotationOptional.get();
@@ -1450,6 +1451,8 @@ private ModelConfigParameter resolveModelConfigParameter(FieldInfo fieldInfo) {
                     schemaTypeAnnotationValue != null ? SchemaType.valueOf(schemaTypeAnnotationValue.asString()) : null;
             AnnotationValue formatAnnotationValue = schemaAnnotation.value("format");
             format = formatAnnotationValue != null ? DataFormat.fromString(formatAnnotationValue.asString()) : null;
+            AnnotationValue nullableAnnotationValue = schemaAnnotation.value("nullable");
+            nullable = nullableAnnotationValue != null && nullableAnnotationValue.asBoolean();
         }
 
         name = name != null ? name : fieldInfo.name();
@@ -1474,7 +1477,7 @@ private ModelConfigParameter resolveModelConfigParameter(FieldInfo fieldInfo) {
         }
 
         return new ModelConfigParameter(name, title, description, kind, type, arrayItemType, format, schemaTypeRef,
-                constraintRef);
+                nullable, constraintRef);
     }
 
     private DocumentationDescriptor processModelDocumentation() {

service/quarkus/deployment/src/test/java/ai/timefold/solver/service/quarkus/deployment/ModelConfigDescriptorSchemaTest.java

@@ -71,6 +71,7 @@ void detectModelConfigOverrides() throws IOException {
             softly.assertThat(primitive.format()).isEqualTo(DataFormat.Percentage);
             softly.assertThat(primitive.kind()).isEqualTo(ParameterKind.PARAMETER);
             softly.assertThat(primitive.type()).isEqualTo(Schema.SchemaType.INTEGER);
+            softly.assertThat(primitive.nullable()).isFalse();
 
             ModelConfigParameter primitiveArray = modelConfigDescriptor.configParameters().get(2);
             softly.assertThat(primitiveArray.id()).isEqualTo("primitiveArrayParam");
@@ -97,6 +98,7 @@ void detectModelConfigOverrides() throws IOException {
             softly.assertThat(string.kind()).isEqualTo(ParameterKind.PARAMETER);
             softly.assertThat(string.type()).isEqualTo(Schema.SchemaType.STRING);
             softly.assertThat(string.schemaTypeRef()).isNull();
+            softly.assertThat(string.nullable()).isTrue();
         });
     }
 }

service/quarkus/deployment/src/test/java/ai/timefold/solver/service/quarkus/deployment/testdata/modelconfigschema/TestdataModelConfigOverrides.java

@@ -25,7 +25,7 @@ public class TestdataModelConfigOverrides implements ModelConfigOverrides {
 
     // Getters added due to serialization in tests when the extension is created (@RegisterExtension)
 
-    @Schema(description = "String parameter")
+    @Schema(description = "String parameter", nullable = true)
     private String string;
 
     public long getConstraintWeight() {