Guard against null parameter fields in OpenAPI operation parsing (#1453)

* Guard against null parameter fields in OpenAPI operation parsing

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

* Guard operation.parameters from NPE

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

* Apply pull request suggestions

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

* Compare enum with == operator

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

* Apply @fjtirado suggestions

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

* Use hasParameters instead != null check

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

---------

Signed-off-by: Matheus Cruz <matheuscruz.dev@gmail.com>

Author: mcruzdev

impl/openapi/src/main/java/io/serverlessworkflow/impl/executors/openapi/OperationDefinition.java

@@ -60,7 +60,7 @@ List<ParameterDefinition> getParameters() {
     List<ParameterDefinition> paramDefinitions = new ArrayList<>();
     if (operation.hasParameters()) {
       for (UnifiedOpenAPI.Parameter parameter : operation.parameters()) {
-        if (parameter.in().equals("body")) {
+        if ("body".equals(parameter.in())) {
           continue; // body parameters are handled separately
         }
 
@@ -70,13 +70,14 @@ List<ParameterDefinition> getParameters() {
       }
     }
 
-    if (openAPI.swaggerVersion().equals(UnifiedOpenAPI.SwaggerVersion.SWAGGER_V2)) {
+    if (openAPI.swaggerVersion() == UnifiedOpenAPI.SwaggerVersion.SWAGGER_V2
+        && operation.hasParameters()) {
       operation.parameters().stream()
-          .filter(p -> p.in().equals("body"))
+          .filter(p -> "body".equals(p.in()))
           .forEach(
               p -> {
                 UnifiedOpenAPI.Schema schema = p.schema();
-                if (schema.hasRef()) {
+                if (schema != null && schema.hasRef()) {
                   String ref = schema.ref();
                   schema = openAPI.resolveSchema(ref);
                 }

impl/openapi/src/main/java/io/serverlessworkflow/impl/executors/openapi/UnifiedOpenAPI.java

@@ -165,7 +165,7 @@ public boolean hasRequestBody() {
     }
   }
 
-  public record Parameter(String name, String in, Boolean required, Schema schema) {}
+  public record Parameter(String name, String in, boolean required, Schema schema) {}
 
   public record RequestBody(Content content) {}