fix typing

Author: SirCotare

src/main/java/it/aboutbits/springboot/testing/validation/core/BaseRuleBuilder.java

@@ -26,7 +26,7 @@
 import java.util.function.Consumer;
 
 @RequiredArgsConstructor
-public abstract class BaseRuleBuilder<R extends BaseRuleBuilder<?>> implements
+public abstract class BaseRuleBuilder<R extends BaseRuleBuilder<R>> implements
         ValidationRulesData,
         BetweenRule<R>,
         FutureRule<R>,
@@ -54,9 +54,10 @@ public void addRule(@NonNull Rule rule) {
         rules.add(rule);
     }
 
-    public BaseRuleBuilder<R> withAdditionalRules(Consumer<BaseRuleBuilder<R>> registrar) {
-        registrar.accept(this);
-        return this;
+    public <T extends BaseRuleBuilder<T>> T withAdditionalRules(Consumer<T> registrar) {
+        var self = (T) this;
+        registrar.accept(self);
+        return self;
     }
 
     public void isCompliant() {

src/test/java/it/aboutbits/springboot/testing/validation/ValidationAssertTest.java

@@ -32,6 +32,7 @@
 import java.time.YearMonth;
 import java.time.ZonedDateTime;
 import java.time.temporal.ChronoUnit;
+import java.util.function.Consumer;
 
 import static it.aboutbits.springboot.testing.validation.ValidationAssertTest.TestValidationAssert.assertThatValidation;
 import static org.assertj.core.api.Assertions.assertThatCode;
@@ -641,6 +642,24 @@ void shouldAlsoWorkForExtendedClassesEvenWithoutAllArgsConstructors() {
                             .isCompliant()
             );
         }
+
+        @Test
+        void usingRuleRegistrarShouldWork() {
+            var item = new SomeExtendingClass();
+            item.notNull = "notNull";
+            item.notNullPositiveOrZero = ScaledBigDecimal.ONE;
+
+            Consumer<TestValidationAssert.TestRuleBuilder> registrar = (ruleBuilder -> ruleBuilder
+                    .notNull("notNull")
+                    .notNull("notNull")
+                    .positiveOrZero("notNullPositiveOrZero")
+            );
+
+            assertThatValidation().of(item)
+                    .usingBeanValidation()
+                    .withAdditionalRules(registrar)
+                    .isCompliant();
+        }
     }
 
     private static SomeValidParameter getSomeValidParameter() {