Better handling of NPE in parser when referencing invalid schema

Created by: zhuangheihei

PR checklist

• Read the contribution guidelines.
• Pull Request title clearly describes the work in the pull request and Pull Request description provides details about how to validate the work. Missing information here may result in delayed response from the community.
• Run the following to build the project and update samples:

  ./mvnw clean package 
  ./bin/generate-samples.sh
  ./bin/utils/export_docs_generators.sh

  Commit all changed files. This is important, as CI jobs will verify all generator outputs of your HEAD commit as it would merge with master. These must match the expectations made by your contribution. You may regenerate an individual generator by passing the relevant config(s) as an argument to the script, for example ./bin/generate-samples.sh bin/configs/java*. For Windows users, please run the script in Git BASH.
• File the PR against the correct branch: master (5.3.0), 6.0.x
• If your PR is targeting a particular programming language, @mention the technical committee members, so they are more likely to review the pull request.

To close https://github.com/OpenAPITools/openapi-generator/issues/10321

modules/openapi-generator/src/main/java/org/openapitools/codegen/config/CodegenConfigurator.java

@@ -534,8 +534,18 @@ public class CodegenConfigurator {
         if (validationMessages.size() > 0) {
             Set<String> warnings = new HashSet<>();
             if (specification != null) {
-                List<String> unusedModels = ModelUtils.getUnusedSchemas(specification);
-                unusedModels.forEach(name -> warnings.add("Unused model: " + name));
+
+                // Wrap the getUnusedSchemas() in try catch block so it catches the NPE
+                // when the input spec file is not correct
+                try{
+                    List<String> unusedModels = ModelUtils.getUnusedSchemas(specification);
+                    if (unusedModels != null) {
+                        unusedModels.forEach(name -> warnings.add("Unused model: " + name));
+                    }
+                } catch (Exception e){
+                    System.err.println("[error] There is an error with OpenAPI specification parsed from the input spec file: " + inputSpec);
+                    System.err.println("[error] Please make sure the spec file has correct format and all required fields are populated with valid value.");
+                }
             }
 
             if (workflowSettings.isValidateSpec()) {

modules/openapi-generator-cli/src/test/java/org/openapitools/codegen/cmd/GenerateTest.java

@@ -22,7 +22,9 @@ import org.apache.commons.lang3.ArrayUtils;
 import org.mockito.MockSettings;
 import org.openapitools.codegen.DefaultGenerator;
 import org.openapitools.codegen.Generator;
+import org.openapitools.codegen.SpecValidationException;
 import org.openapitools.codegen.config.CodegenConfigurator;
+import org.testng.TestException;
 import org.testng.annotations.AfterMethod;
 import org.testng.annotations.BeforeMethod;
 import org.testng.annotations.Test;
@@ -430,4 +432,12 @@ public class GenerateTest {
         verify(configurator).toContext();
         verifyNoMoreInteractions(configurator);
     }
+
+    /**
+     * This test ensures that when the
+     */
+    @Test(expectedExceptions = SpecValidationException.class)
+    public void testNPEWithInvalidSpecFile() {
+        setupAndRunTest("-i", "src/test/resources/npe-test.yaml", "-g", "java", "-o", "src/main/java", false, null);
+    }
 }

modules/openapi-generator-cli/src/test/resources/npe-test-spec-file.yaml

+test:
+  get:
+    responses:
+      '200':
+        description: test
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                prop1:
+                  type: array
+                prop2:
+                  type: date
\ No newline at end of file

modules/openapi-generator-cli/src/test/resources/npe-test.yaml

+openapi: 3.0.0
+info:
+  description: test
+  version: test
+  title: test
+paths:
+  /test:
+    $ref: 'npe-test-spec-file.yaml#/test'
\ No newline at end of file