fix enum type comparison for string

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

@@ -5306,7 +5306,7 @@ public class DefaultCodegen implements CodegenConfig {
         if (var.defaultValue != null) {
             String enumName = null;
             final String enumDefaultValue;
-            if ("string".equalsIgnoreCase(dataType)) {
+            if (typeMapping.get("string").equalsIgnoreCase(dataType)) {
                 enumDefaultValue = toEnumValue(var.defaultValue, dataType);
             } else {
                 enumDefaultValue = var.defaultValue;

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

@@ -158,6 +158,8 @@ public class NimClientCodegen extends DefaultCodegen implements CodegenConfig {
         typeMapping.put("DateTime", "string");
         typeMapping.put("password", "string");
         typeMapping.put("file", "string");
+        typeMapping.put("string", "string");
+
     }
 
     public void setPackageName(String packageName) {