fix issue when discriminator property is an enum string (#13001)

samples/client/petstore/java/okhttp-gson/docs/EnumStringDiscriminator.md

@@ -0,0 +1,23 @@
+
+
+# EnumStringDiscriminator
+
+An object to test discriminator of enum string
+
+## Properties
+
+| Name | Type | Description | Notes |
+|------------ | ------------- | ------------- | -------------|
+|**enumStrType** | [**EnumStrTypeEnum**](#EnumStrTypeEnum) | enum string type |  |
+
+
+
+## Enum: EnumStrTypeEnum
+
+| Name | Value |
+|---- | -----|
+| A | "type_a" |
+| B | "type_b" |
+
+
+