Better handling of NPE in parser when referencing invalid schema (#10882)

* try to catch NullPointerException and print error message

* handles invalid specifications when the spec file is invalid

* added comment

* added null pointer exception test

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

@@ -0,0 +1,14 @@
+test:
+  get:
+    responses:
+      '200':
+        description: test
+        content:
+          application/json:
+            schema:
+              type: object
+              properties:
+                prop1:
+                  type: array
+                prop2:
+                  type: date

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

@@ -0,0 +1,8 @@
+openapi: 3.0.0
+info:
+  description: test
+  version: test
+  title: test
+paths:
+  /test:
+    $ref: 'npe-test-spec-file.yaml#/test'

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()) {