[GO] fix: stops checking for nil for structs (#13843)

* [GO] fix: stops checking for nil for structs

* [GO] chore: regenerates samples

Author: NickUfer

modules/openapi-generator/src/main/resources/go/model_simple.mustache

@@ -122,8 +122,13 @@ func (o *{{classname}}) Get{{name}}() {{vendorExtensions.x-go-base-type}} {
 // Deprecated
 {{/deprecated}}
 func (o *{{classname}}) Get{{name}}Ok() ({{^isArray}}{{^isFreeFormObject}}*{{/isFreeFormObject}}{{/isArray}}{{vendorExtensions.x-go-base-type}}, bool) {
-	if o == nil{{#isNullable}}{{#vendorExtensions.x-golang-is-container}} || o.{{name}} == nil{{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
-		return nil, false
+	if o == nil{{#isNullable}}{{#vendorExtensions.x-golang-is-container}} || isNil(o.{{name}}){{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
+{{^isFreeFormObject}}
+    return nil, false
+    {{/isFreeFormObject}}
+    {{#isFreeFormObject}}
+    return {{vendorExtensions.x-go-base-type}}{}, false
+    {{/isFreeFormObject}}
 	}
 {{#isNullable}}
 {{#vendorExtensions.x-golang-is-container}}
@@ -163,7 +168,7 @@ func (o *{{classname}}) Set{{name}}(v {{vendorExtensions.x-go-base-type}}) {
 // Deprecated
 {{/deprecated}}
 func (o *{{classname}}) Get{{name}}() {{vendorExtensions.x-go-base-type}} {
-	if o == nil{{^isNullable}} || o.{{name}} == nil{{/isNullable}}{{#isNullable}}{{^vendorExtensions.x-golang-is-container}} || o.{{name}}.Get() == nil{{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
+	if o == nil{{^isNullable}} || isNil(o.{{name}}){{/isNullable}}{{#isNullable}}{{^vendorExtensions.x-golang-is-container}} || isNil(o.{{name}}.Get()){{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
 		var ret {{vendorExtensions.x-go-base-type}}
 		return ret
 	}
@@ -189,8 +194,13 @@ func (o *{{classname}}) Get{{name}}() {{vendorExtensions.x-go-base-type}} {
 // Deprecated
 {{/deprecated}}
 func (o *{{classname}}) Get{{name}}Ok() ({{^isArray}}{{^isFreeFormObject}}*{{/isFreeFormObject}}{{/isArray}}{{vendorExtensions.x-go-base-type}}, bool) {
-	if o == nil{{^isNullable}} || o.{{name}} == nil{{/isNullable}}{{#isNullable}}{{#vendorExtensions.x-golang-is-container}} || o.{{name}} == nil{{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
-		return nil, false
+	if o == nil{{^isNullable}} || isNil(o.{{name}}){{/isNullable}}{{#isNullable}}{{#vendorExtensions.x-golang-is-container}} || isNil(o.{{name}}){{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
+    {{^isFreeFormObject}}
+    return nil, false
+    {{/isFreeFormObject}}
+    {{#isFreeFormObject}}
+    return {{vendorExtensions.x-go-base-type}}{}, false
+    {{/isFreeFormObject}}
 	}
 {{#isNullable}}
 {{#vendorExtensions.x-golang-is-container}}
@@ -207,7 +217,7 @@ func (o *{{classname}}) Get{{name}}Ok() ({{^isArray}}{{^isFreeFormObject}}*{{/is
 
 // Has{{name}} returns a boolean if a field has been set.
 func (o *{{classname}}) Has{{name}}() bool {
-	if o != nil && {{^isNullable}}o.{{name}} != nil{{/isNullable}}{{#isNullable}}{{#vendorExtensions.x-golang-is-container}}o.{{name}} != nil{{/vendorExtensions.x-golang-is-container}}{{^vendorExtensions.x-golang-is-container}}o.{{name}}.IsSet(){{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
+	if o != nil && {{^isNullable}}!isNil(o.{{name}}){{/isNullable}}{{#isNullable}}{{#vendorExtensions.x-golang-is-container}}isNil(o.{{name}}){{/vendorExtensions.x-golang-is-container}}{{^vendorExtensions.x-golang-is-container}}o.{{name}}.IsSet(){{/vendorExtensions.x-golang-is-container}}{{/isNullable}} {
 		return true
 	}
 
@@ -285,7 +295,7 @@ func (o {{classname}}) MarshalJSON() ([]byte, error) {
 	{{/isNullable}}
 	{{! if argument is not nullable, don't set it if it is nil}}
 	{{^isNullable}}
-	if {{#required}}true{{/required}}{{^required}}o.{{name}} != nil{{/required}} {
+	if {{#required}}true{{/required}}{{^required}}!isNil(o.{{name}}){{/required}} {
 		toSerialize["{{baseName}}"] = o.{{name}}
 	}
 	{{/isNullable}}

modules/openapi-generator/src/main/resources/go/utils.mustache

@@ -3,6 +3,7 @@ package {{packageName}}
 
 import (
 	"encoding/json"
+    "reflect"
 	"time"
 )
 
@@ -317,3 +318,17 @@ func (v *NullableTime) UnmarshalJSON(src []byte) error {
 	v.isSet = true
 	return json.Unmarshal(src, &v.value)
 }
+
+// isNil checks if an input is nil
+func isNil(i interface{}) bool {
+    if i == nil {
+        return true
+    }
+    switch reflect.TypeOf(i).Kind() {
+    case reflect.Chan, reflect.Func, reflect.Map, reflect.Ptr, reflect.UnsafePointer, reflect.Interface, reflect.Slice:
+        return reflect.ValueOf(i).IsNil()
+    case reflect.Array:
+        return reflect.ValueOf(i).IsZero()
+    }
+    return false
+}