fix NPE when parsing V2 with OpenAPIV3Parser and resolveFully option

Avoid to resolve openAPI if it is null
Fixes #1455

Author: phiz71

modules/swagger-parser-v3/src/main/java/io/swagger/v3/parser/OpenAPIV3Parser.java

@@ -150,7 +150,10 @@ private SwaggerParseResult readContents(String swaggerAsString, List<Authorizati
             final ObjectMapper mapper = getRightMapper(swaggerAsString);
             final JsonNode rootNode = mapper.readTree(swaggerAsString);
             final SwaggerParseResult result = parseJsonNode(location, rootNode);
-            return resolve(result, auth, options, location);
+            if (result.getOpenAPI() != null) {
+                return resolve(result, auth, options, location);
+            }
+            return result;
         } catch (JsonProcessingException e) {
             LOGGER.warn("Exception while parsing:", e);
             final String message = getParseErrorMessage(e.getOriginalMessage(), location);

modules/swagger-parser-v3/src/test/java/io/swagger/v3/parser/test/OpenAPIV3ParserTest.java

@@ -878,6 +878,22 @@ public void testResolveFully() throws Exception{
         assertEquals(result.getOpenAPI().getComponents().getSchemas().get("OrderRef").getType(),"object");
     }
 
+    @Test
+    public void issue1455_testResolveFullyV2_shouldNotThrowNPE() throws Exception{
+        String pathFile = FileUtils.readFileToString(new File("src/test/resources/swagger.json"));
+        pathFile = pathFile.replace("${dynamicPort}", String.valueOf(this.serverPort));
+        ParseOptions options = new ParseOptions();
+        options.setResolveFully(true);
+
+        SwaggerParseResult result = new OpenAPIV3Parser().readContents(pathFile, new ArrayList<>(), options  );
+
+        Assert.assertNotNull(result);
+        Assert.assertNull(result.getOpenAPI());
+        Assert.assertNotNull(result.getMessages());
+        Assert.assertEquals(result.getMessages().size(), 1);
+        Assert.assertEquals(result.getMessages().get(0), "attribute openapi is missing");
+    }
+
     @Test
     public void testResolveEmpty(@Injectable final List<AuthorizationValue> auths) throws Exception{
         String pathFile = FileUtils.readFileToString(new File("src/test/resources/empty-oas.yaml"));