fix and test for issue #404 NullExample

pom.xml

@@ -461,7 +461,7 @@
     <properties>
         <maven-javadoc-version>3.0.1</maven-javadoc-version>
         <swagger-core-version>2.1.10</swagger-core-version>
-        <swagger-parser-version>2.0.27</swagger-parser-version>
+        <swagger-parser-version>2.0.28-SNAPSHOT</swagger-parser-version>
         <jackson.version>2.12.1</jackson.version>
         <jetty-version>9.4.39.v20210325</jetty-version>
         <jersey2-version>2.32</jersey2-version>

src/test/java/io/swagger/oas/test/examples/ExampleBuilderTest.java

@@ -67,6 +67,22 @@ public class ExampleBuilderTest {
         Yaml.mapper().registerModule(simpleModule);
     }
 
+    @Test
+    public void testIssue404_NullExample(){
+        ParseOptions options = new ParseOptions();
+        options.setResolveFully(true);
+
+        OpenAPI openAPI = new OpenAPIV3Parser().read("src/test/swagger/sampleNull.json", null, options);
+        Example example = ExampleBuilder.fromSchema(openAPI.getComponents().getSchemas().get("Bundle"), openAPI.getComponents().getSchemas());
+        String json = Json.pretty(example);
+        assertEquals(json,"{\n" +
+                        "  \"_id\" : \"string\",\n" +
+                        "  \"project_id\" : \"string\",\n" +
+                        "  \"href\" : \"string\",\n" +
+                        "  \"name\" : \"string\"\n" +
+                        "}");
+    }
+
     @Test
     public void testAnonymousModel(){
         ParseOptions options = new ParseOptions();

src/test/swagger/sampleNull.json

@@ -0,0 +1,175 @@
+{
+  "swagger": "2.0",
+  "info": {
+    "description": "Blah",
+    "version": "1.0.0",
+    "title": "Blah",
+    "termsOfService": "",
+    "contact": {
+      "email": ""
+    },
+    "license": {
+      "name": "",
+      "url": "http://unlicense.org"
+    }
+  },
+  "basePath": "/rest",
+  "tags": [
+  ],
+  "paths": {
+    "/v1/tx/packages/{package_id}": {
+      "get": {
+        "tags": [
+          "Packages"
+        ],
+        "summary": "Get a package",
+        "description": "Get details about a package",
+        "operationId": "getPackage",
+        "produces": [
+          "application/json;charset=utf-8"
+        ],
+        "parameters": [
+          {
+            "name": "package_id",
+            "in": "path",
+            "description": "ID of the package",
+            "required": true,
+            "type": "string"
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Error",
+            "schema": {
+              "$ref": "#/definitions/Bundle"
+            }
+          }
+        }
+      },
+      "put": {
+        "tags": [
+          "Packages"
+        ],
+        "summary": "Edit a package definition",
+        "description": "Replace package definition",
+        "operationId": "replacePackage",
+        "consumes": [
+          "application/json;charset=utf-8"
+        ],
+        "produces": [
+          "application/json;charset=utf-8"
+        ],
+        "parameters": [
+          {
+            "name": "package_id",
+            "in": "path",
+            "description": "ID of the package",
+            "required": true,
+            "type": "string"
+          },
+          {
+            "in": "body",
+            "name": "body",
+            "description": "Package definition.",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/Bundle"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "Error",
+            "schema": {
+              "$ref": "#/definitions/Bundle"
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "schema": {
+              "$ref": "#/definitions/Bundle"
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "schema": {
+              "$ref": "#/definitions/Bundle"
+            }
+          }
+        }
+      },
+      "delete": {
+        "tags": [
+          "Packages"
+        ],
+        "summary": "Delete a package",
+        "description": "Remove a package",
+        "operationId": "deletePackage",
+        "produces": [
+          "application/json;charset=utf-8"
+        ],
+        "parameters": [
+          {
+            "name": "package_id",
+            "in": "path",
+            "description": "ID of the package",
+            "required": true,
+            "type": "string"
+          }
+        ],
+        "responses": {
+          "204": {
+            "description": "Success"
+          },
+          "401": {
+            "description": "Unauthorized"
+          },
+          "403": {
+            "description": "Forbidden"
+          },
+          "200": {
+            "description": "Error"
+          }
+        }
+      }
+    }
+  },
+  "definitions": {
+    "Annotation": {
+      "type": "object",
+      "properties": {
+        "name": {
+          "type": "string",
+          "description": "Annotation name"
+        },
+        "value": {
+          "type": "string",
+          "description": "Annotation value"
+        }
+      },
+      "description": "Resource annotation"
+    },
+    "Bundle": {
+      "type": "object",
+      "properties": {
+        "_id": {
+          "type": "string",
+          "description": "The id of the object"
+        },
+        "project_id": {
+          "type": "string",
+          "description": "The project id of the map or file"
+        },
+        "href": {
+          "type": "string",
+          "description": "The URI for the object"
+        },
+        "name": {
+          "type": "string",
+          "description": "Name of the package"
+        }
+      }
+    },
+    "description": "A bundle (package)"
+  }
+}