Fix OpenAPI 3.0 output of nullable references

core/src/main/java/io/smallrye/openapi/runtime/io/media/SchemaIO.java

@@ -191,7 +191,7 @@ private void populateSchemaObject30(Schema schema, O node) {
         }
 
         // Detect {$ref=....,nullable=true} and convert to anyOf[{$ref=...}, {type=null}]
-        if (schema.getRef() != null && schema.getType() == null && SchemaSupport.getNullable(schema) == Boolean.TRUE) {
+        if (schema.getRef() != null && SchemaSupport.getNullable(schema) == Boolean.TRUE) {
             List<Schema> newAnyOfSchemas = new ArrayList<>();
             newAnyOfSchemas.add(OASFactory.createSchema().ref(schema.getRef()));
             newAnyOfSchemas.add(SchemaSupport.nullSchema());
@@ -201,7 +201,11 @@ private void populateSchemaObject30(Schema schema, O node) {
                 schema.addAllOf(OASFactory.createSchema().anyOf(newAnyOfSchemas));
             }
             schema.setRef(null);
-            SchemaSupport.setNullable(schema, null);
+            if (schema.getType() == null) {
+                SchemaSupport.setNullable(schema, null);
+            } else {
+                SchemaSupport.setNullable(schema, Boolean.TRUE);
+            }
         }
 
         // Detect {enum=[null]} and convert to {type=null}
@@ -389,7 +393,7 @@ private ReplacementFields compute30ReplacementFields(Schema schema31) {
         }
 
         // If we have anyOf = [{type=null}, {$ref=...}], remove it and set nullable and allOf = [{$ref=...}]
-        if (result.anyOf != null && result.anyOf.size() == 2 && result.ref == null && result.type == null) {
+        if (result.anyOf != null && result.anyOf.size() == 2 && result.ref == null) {
             Optional<Schema> typeNullSchema = result.anyOf.stream().filter(s -> isSoloTypeNull(s)).findFirst();
             Optional<Schema> refSchema = result.anyOf.stream().filter(s -> isSoloRef(s)).findFirst();
             if (typeNullSchema.isPresent() && refSchema.isPresent()) {

core/src/test/java/io/smallrye/openapi/runtime/scanner/SchemaPropertyTest.java

@@ -93,4 +93,29 @@ static class Turtle extends Reptile {
         String shellPattern;
         Speed speed;
     }
+
+    @Test
+    void testNullableFieldReference() throws Exception {
+        Index index = indexOf(FieldTarget.class, FieldReferrer.class);
+        SmallRyeOpenAPI result1 = SmallRyeOpenAPI.builder()
+                .withConfig(config(Collections.emptyMap()))
+                .withIndex(index)
+                .defaultRequiredProperties(false)
+                .build();
+        printToConsole(result1.model());
+        assertJsonEquals("components.schemas.schemaproperty-nullable.json", result1.model());
+    }
+
+    @org.eclipse.microprofile.openapi.annotations.media.Schema
+    public static class FieldTarget {
+    }
+
+    @org.eclipse.microprofile.openapi.annotations.media.Schema
+    public static class FieldReferrer {
+        @org.eclipse.microprofile.openapi.annotations.media.Schema(nullable = true)
+        private FieldTarget a;
+        @org.eclipse.microprofile.openapi.annotations.media.Schema(nullable = true, description = "b")
+        private FieldTarget b;
+    }
+
 }

core/src/test/resources/io/smallrye/openapi/runtime/io/schemas-with-nullable-reference.json

@@ -13,6 +13,18 @@
           }
         ]
       },
+      "NullRefWithAnnotations": {
+        "description": "Description is an annotation. Scanner generates type as well here.",
+        "type": ["object", "null"],
+        "anyOf": [
+          {
+            "$ref": "#/components/schemas/mySchema"
+          },
+          {
+            "type": "null"
+          }
+        ]
+      },
       "NullRefWithAnyOf": {
         "allOf": [
           {

core/src/test/resources/io/smallrye/openapi/runtime/io/schemas-with-nullable-reference30.json

@@ -11,6 +11,16 @@
           }
         ]
       },
+      "NullRefWithAnnotations": {
+        "description": "Description is an annotation. Scanner generates type as well here.",
+        "type": "object",
+        "allOf": [
+          {
+            "$ref": "#/components/schemas/mySchema"
+          }
+        ],
+        "nullable": true
+      },
       "NullRefWithAnyOf": {
         "allOf": [
           {

core/src/test/resources/io/smallrye/openapi/runtime/scanner/components.schemas.schemaproperty-nullable.json

@@ -0,0 +1,31 @@
+{
+  "openapi" : "3.1.0",
+  "components" : {
+    "schemas" : {
+      "FieldReferrer" : {
+        "type" : "object",
+        "properties" : {
+          "a" : {
+            "anyOf" : [ {
+              "$ref" : "#/components/schemas/FieldTarget"
+            }, {
+              "type" : "null"
+            } ]
+          },
+          "b" : {
+            "description" : "b",
+            "type" : "object",
+            "anyOf" : [ {
+              "$ref" : "#/components/schemas/FieldTarget"
+            }, {
+              "type" : "null"
+            } ]
+          }
+        }
+      },
+      "FieldTarget" : {
+        "type" : "object"
+      }
+    }
+  }
+}