[Java] add missing nullable judgement when required property is true

Author: fanqiewanzi

modules/openapi-generator/src/main/resources/Java/libraries/okhttp-gson/pojo.mustache

@@ -398,7 +398,7 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{#items.isModel}}
       {{#required}}
       // ensure the json data is an array
-      if (!jsonObj.get("{{{baseName}}}").isJsonArray()) {
+      if (!jsonObj.get("{{{baseName}}}").isJsonArray(){{#isNullable}} && !jsonObj.get("{{baseName}}").isJsonNull(){{/isNullable}}) {
         throw new IllegalArgumentException(String.format("Expected the field `{{{baseName}}}` to be an array in the JSON string but got `%s`", jsonObj.get("{{{baseName}}}").toString()));
       }
 
@@ -436,7 +436,7 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       // ensure the required json array is present
       if (jsonObj.get("{{{baseName}}}") == null) {
         throw new IllegalArgumentException("Expected the field `linkedContent` to be an array in the JSON string but got `null`");
-      } else if (!jsonObj.get("{{{baseName}}}").isJsonArray()) {
+      } else if (!jsonObj.get("{{{baseName}}}").isJsonArray(){{#isNullable}} && !jsonObj.get("{{baseName}}").isJsonNull(){{/isNullable}}) {
         throw new IllegalArgumentException(String.format("Expected the field `{{{baseName}}}` to be an array in the JSON string but got `%s`", jsonObj.get("{{{baseName}}}").toString()));
       }
       {{/required}}
@@ -450,8 +450,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isString}}
       {{#isModel}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{dataType}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`
@@ -462,8 +468,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isModel}}
       {{#isEnum}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{datatypeWithEnum}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`
@@ -474,8 +486,14 @@ public class {{classname}} {{#parent}}extends {{{.}}} {{/parent}}{{#vendorExtens
       {{/isEnum}}
       {{#isEnumRef}}
       {{#required}}
+      {{#isNullable}}
+      if (jsonObj.get("{{{baseName}}}") != null && !jsonObj.get("{{{baseName}}}").isJsonNull()) {
+      {{/isNullable}}
       // validate the required field `{{{baseName}}}`
       {{{dataType}}}.validateJsonElement(jsonObj.get("{{{baseName}}}"));
+      {{#isNullable}}
+      }
+      {{/isNullable}}
       {{/required}}
       {{^required}}
       // validate the optional field `{{{baseName}}}`