Use empty message for Non-Spring Boot Condition

Update `AbstractNestedCondition` to use an empty message for non
Spring Boot nested conditions.

Fixes gh-7519
Closes gh-7529

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/AbstractNestedCondition.java

@@ -195,7 +195,7 @@ abstract class AbstractNestedCondition extends SpringBootCondition
 						metadata);
 			}
 			return new ConditionOutcome(condition.matches(this.context, metadata),
-					(ConditionMessage) null);
+					ConditionMessage.empty());
 		}
 
 		public ConditionOutcome getUltimateOutcome() {

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/AllNestedConditionsTests.java

@@ -21,8 +21,11 @@ import org.junit.Test;
 import org.springframework.boot.test.util.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Condition;
+import org.springframework.context.annotation.ConditionContext;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.type.AnnotatedTypeMetadata;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -94,6 +97,20 @@ public class AllNestedConditionsTests {
 
 		}
 
+		@Conditional(NonSpringBootCondition.class)
+		static class SubclassC {
+
+		}
+
+	}
+
+	static class NonSpringBootCondition implements Condition {
+
+		@Override
+		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+			return true;
+		}
+
 	}
 
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/AnyNestedConditionTests.java

@@ -21,8 +21,11 @@ import org.junit.Test;
 import org.springframework.boot.test.util.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Condition;
+import org.springframework.context.annotation.ConditionContext;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.type.AnnotatedTypeMetadata;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -98,6 +101,20 @@ public class AnyNestedConditionTests {
 
 		}
 
+		@Conditional(NonSpringBootCondition.class)
+		static class SubclassC {
+
+		}
+
+	}
+
+	static class NonSpringBootCondition implements Condition {
+
+		@Override
+		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+			return false;
+		}
+
 	}
 
 }

spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/condition/NoneNestedConditionsTests.java

@@ -21,8 +21,11 @@ import org.junit.Test;
 import org.springframework.boot.test.util.EnvironmentTestUtils;
 import org.springframework.context.annotation.AnnotationConfigApplicationContext;
 import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Condition;
+import org.springframework.context.annotation.ConditionContext;
 import org.springframework.context.annotation.Conditional;
 import org.springframework.context.annotation.Configuration;
+import org.springframework.core.type.AnnotatedTypeMetadata;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -94,6 +97,20 @@ public class NoneNestedConditionsTests {
 
 		}
 
+		@Conditional(NonSpringBootCondition.class)
+		static class SubClassC {
+
+		}
+
+	}
+
+	static class NonSpringBootCondition implements Condition {
+
+		@Override
+		public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
+			return false;
+		}
+
 	}
 
 }