Fix validation of Set values

Since commit 8552e14, validation of Set values
(for example `Set<@notblank String>`) crashes with error :
No way to unwrap Iterable without index

With this fix we don't know which value exactly is the problem, but at least we
have a working validation

spring-context/src/main/java/org/springframework/validation/beanvalidation/MethodValidationAdapter.java

@@ -346,6 +346,10 @@ else if (key != null && arg instanceof Map<?, ?> map) {
 					value = map.get(key);
 					container = map;
 				}
+				else if (arg instanceof Set<?>) {
+					value = arg;
+					container = null;
+				}
 				else if (arg instanceof Optional<?> optional) {
 					value = optional.orElse(null);
 					container = optional;

spring-context/src/test/java/org/springframework/validation/beanvalidation/MethodValidationAdapterTests.java

@@ -19,6 +19,7 @@
 import java.lang.reflect.Method;
 import java.util.List;
 import java.util.Locale;
+import java.util.Set;
 import java.util.function.Consumer;
 
 import jakarta.validation.Valid;
@@ -39,6 +40,7 @@
 import org.springframework.validation.method.ParameterValidationResult;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.InstanceOfAssertFactories.SET;
 
 /**
  * Tests for {@link MethodValidationAdapter}.
@@ -213,6 +215,24 @@ void validateValueListArgument() {
 		});
 	}
 
+	@Test
+	void validateValueSetArgument() {
+		MyService target = new MyService();
+		Method method = getMethod(target, "addUniqueHobbies");
+
+		testArgs(target, method, new Object[] {Set.of("test", "   ")}, ex -> {
+
+			assertThat(ex.getAllValidationResults()).hasSize(1);
+
+			assertValueResult(ex.getValueResults().get(0), 0, Set.of("test", "   "), List.of("""
+				org.springframework.context.support.DefaultMessageSourceResolvable: \
+				codes [NotBlank.myService#addUniqueHobbies.hobbies,NotBlank.hobbies,NotBlank.java.util.Set,NotBlank]; \
+				arguments [org.springframework.context.support.DefaultMessageSourceResolvable: \
+				codes [myService#addUniqueHobbies.hobbies,hobbies]; \
+				arguments []; default message [hobbies]]; default message [must not be blank]"""));
+		});
+	}
+
 	private void testArgs(Object target, Method method, Object[] args, Consumer<MethodValidationResult> consumer) {
 		consumer.accept(this.validationAdapter.validateArguments(target, method, null, args, new Class<?>[0]));
 	}
@@ -271,6 +291,8 @@ public void addPeople(@Valid List<Person> people) {
 		public void addHobbies(List<@NotBlank String> hobbies) {
 		}
 
+		public void addUniqueHobbies(Set<@NotBlank String> hobbies) {
+		}
 	}