[JAVA] Generated code for petstore3 uses invalid base path for API calls

Description

I'm using swagger-codegen-cli to generate code from the petstore3 declaration file. I was invoking the code generator with -i https://petstore3.swagger.io/api/v3/openapi.json which worked perfectly fine, however, when I used a downloaded version of the json file and invoke it with -i petstore3_openapi.json (downloaded from https://petstore3.swagger.io/api/v3/openapi.json), it wouldn't work anymore and give me this stacktrace:

java.lang.IllegalArgumentException: unexpected url: /api/v3/pet/1
	at com.squareup.okhttp.Request$Builder.url(Request.java:163)
	at openapi.petStoreclient.ApiClient.buildRequest(ApiClient.java:971)
	at openapi.petStoreclient.ApiClient.buildCall(ApiClient.java:947)
	at openapi.petStoreclient.apis.PetApi.getPetByIdCall(PetApi.java:777)
	at openapi.petStoreclient.apis.PetApi.getPetByIdValidateBeforeCall(PetApi.java:787)
	at openapi.petStoreclient.apis.PetApi.getPetByIdWithHttpInfo(PetApi.java:816)
	at openapi.petStoreclient.apis.PetApi.getPetById(PetApi.java:804)

See in the Suggest a fix/enhancement section below to find my speculations.

Swagger-codegen version

3.0.36

Swagger declaration file content or url

https://petstore3.swagger.io/api/v3/openapi.json

Command line used for generation

java -jar swagger-codegen-cli-3.0.36.jar generate -i openapi.json -l java -o petstore-client

Steps to reproduce

wget https://repo1.maven.org/maven2/io/swagger/codegen/v3/swagger-codegen-cli/3.0.36/swagger-codegen-cli-3.0.36.jar

wget https://petstore3.swagger.io/api/v3/openapi.json

java -jar swagger-codegen-cli-3.0.36.jar generate -i openapi.json -l java -o petstore-client

4. Execute this Java code snippet

try {
    new PetApi().getPetById(1L);
} catch (ApiException e) {
    throw new RuntimeException(e);
}

5. You should see the stacktrace from the Description section

Related issues/PRs

Suggest a fix/enhancement

I do not have a suggestion. It seems to me that it stems from defining servers.0.url = "api/v3" instead of "https://petstore3.swagger.io/api/v3" in the declaration file which causes the field basePath in ApiClient.java to become that url.
Perhaps I'm missing something here and this is desired behavior. Thanks in advance for any help.

Reproduce the issue with the downloaded openapi.json and the swagger-codegen-cli 3.0.36 command. Start by inspecting the generated ApiClient.java basePath handling and the PetApi.java call shown in the stack trace; done means the generated client can execute getPetById with a valid request URL in both input-file scenarios.