fix(avro-schema): fix NPE for null enum values

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

@@ -6648,7 +6648,7 @@ protected List<Map<String, Object>> buildEnumVars(List<Object> values, String da
         for (Object value : values) {
             if (value == null) {
                 // raw null values in enums are unions for nullable
-                // atttributes, not actual enum values, so we remove them here
+                // attributes, not actual enum values, so we remove them here
                 continue;
             }
             Map<String, Object> enumVar = new HashMap<>();

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/AvroSchemaCodegen.java

@@ -199,8 +199,11 @@ public String escapeQuotationMark(String input) {
 
     @Override
     protected List<Map<String, Object>> buildEnumVars(List<Object> values, String dataType) {
-        List<Object> sanitizedValues = values.stream().map(Object::toString).map(this::sanitizeEnumValue)
-                .collect(Collectors.toList());
+        List<Object> sanitizedValues = values.stream()
+            .filter(x -> x != null)
+            .map(Object::toString)
+            .map(this::sanitizeEnumValue)
+            .collect(Collectors.toList());
         removeEnumValueCollisions(sanitizedValues);
         return super.buildEnumVars(sanitizedValues, dataType);
     }

modules/openapi-generator/src/test/resources/3_0/avro-schema/valid-enums.yaml

@@ -27,4 +27,16 @@ components:
             # The next two is to make sure collisions are resolved properly
             - 'coll-ision'
             - 'coll_ision'
-          type: 'string'
+          type: 'string'
+        another:
+          enum:
+            - 'x'
+            - 'y'
+            - null
+          type: 'string'
+        equivalent:
+          enum:
+            - 'x'
+            - 'y'
+          type: 'string'
+          nullable: true

samples/openapi3/schema/valid-enums/avro-schema-enum/Sample.avsc

@@ -20,6 +20,32 @@
       }],
       "doc": "",
       "default": null
+    },
+    {
+      "name": "another",
+      "type": ["null", {
+        "type": "enum",
+        "name": "Sample_another",
+        "symbols": [
+          "x",
+          "y"
+        ]
+      }],
+      "doc": "",
+      "default": null
+    },
+    {
+      "name": "equivalent",
+      "type": ["null", {
+        "type": "enum",
+        "name": "Sample_equivalent",
+        "symbols": [
+          "x",
+          "y"
+        ]
+      }],
+      "doc": "",
+      "default": null
     }
   ]