fix(core): SchemaObjectBuilder.type(String) is null safe (#1507)

* fix(core): SchemaObjectBuilder.type(String) is null safe

Co-authored-by: Timon Back <[email protected]>

* test(core): Add `@Schema` annotation in combination with `@JsonSubTypes`

---------

Co-authored-by: Timon Back <[email protected]>

Author: sam0r040

springwolf-asyncapi/src/main/java/io/github/springwolf/asyncapi/v3/model/schema/SchemaObject.java

@@ -162,7 +162,9 @@ public SchemaObjectBuilder type(Set<String> type) {
         }
 
         public SchemaObjectBuilder type(String type) {
-            this.type = Set.of(type);
+            if (type != null) {
+                this.type = Set.of(type);
+            }
             return this;
         }
     }

springwolf-core/src/test/java/io/github/springwolf/core/integrationtests/application/polymorphic/PolymorphicPayloadApplication.java

@@ -5,6 +5,7 @@
 import com.fasterxml.jackson.annotation.JsonTypeInfo;
 import io.github.springwolf.core.asyncapi.annotations.AsyncListener;
 import io.github.springwolf.core.asyncapi.annotations.AsyncOperation;
+import io.swagger.v3.oas.annotations.media.Schema;
 import org.springframework.boot.autoconfigure.SpringBootApplication;
 import org.springframework.context.annotation.Bean;
 
@@ -28,6 +29,7 @@ public record Payload(Pet pet) {}
                 @JsonSubTypes.Type(value = Dog.class, name = "dog"),
                 @JsonSubTypes.Type(value = Cat.class, name = "cat"),
             })
+    @Schema(oneOf = {Dog.class, Cat.class})
     public interface Pet {
         String getType();
     }