add a CLI option

Author: vvb

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

@@ -451,4 +451,6 @@ public static enum ENUM_PROPERTY_NAMING_TYPE {camelCase, PascalCase, snake_case,
     public static final String MAX_ATTEMPTS_FOR_RETRY = "maxAttemptsForRetry";
 
     public static final String WAIT_TIME_OF_THREAD = "waitTimeMillis";
+
+    public static final String USE_DEFAULT_VALUES_FOR_REQUIRED_VARS = "useDefaultValuesForRequiredVars";
 }

modules/openapi-generator/src/test/java/org/openapitools/codegen/options/GoClientOptionsProvider.java

@@ -65,6 +65,7 @@ public Map<String, String> createOptions() {
                 .put(CodegenConstants.GENERATE_UNMARSHAL_JSON, "true")
                 .put("generateInterfaces", "true")
                 .put("structPrefix", "true")
+                .put(CodegenConstants.USE_DEFAULT_VALUES_FOR_REQUIRED_VARS, "true")
                 .build();
     }