[GO] Default time fails generation

Created by: eak24

Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• Have you tested with the latest master to confirm the issue still exists?
• Have you searched for related issues/PRs?
• What's the actual output vs expected output?

Description

@knazarenko-ptc and I found that a spec generated with the following bit causes a failure in the generator. The error pops up because this cast to string fails: https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/GoClientCodegen.java#L353 . Should this work?

OpenAPI declaration file content or url

{
        "name": "timeQuery",
        "in": "query",
        "schema": {
          "type": "string",
          "format": "date-time",
          "default": "2000-01-01T00:00:00Z"
        }
      }

Suggest a fix

The fix we have working locally is to call the toString() method on the default object:

diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/GoClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/GoClientCodegen.java
index ed5418ab4a3..f22c18fb13b 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/GoClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/GoClientCodegen.java
@@ -349,8 +349,12 @@ public class GoClientCodegen extends AbstractGoCodegen {
     public String toDefaultValue(Schema p) {
         p = ModelUtils.getReferencedSchema(this.openAPI, p);
         if (ModelUtils.isStringSchema(p)) {
-            if (p.getDefault() != null) {
-                return "\"" + escapeText((String) p.getDefault()) + "\"";
+            Object defaultObj = p.getDefault();
+            if (defaultObj != null) {
+                if (defaultObj instanceof java.lang.String) {
+                    return "\"" + escapeText((String) defaultObj) + "\"";
+                }
+                return "\"" + escapeText(defaultObj.toString()) + "\"";
             }
             return null;
         }