[JAVA] Import mapping don't affect API generated classes in swagger codegen 2.4.7

Description

I have an Api that use java.time.Instant as request parameter.

@GetMapping("/employees/search")
Resources<Employee> search(@RequestParam(name ="Search after", defaultValue =  "2019-07-16T07:30:00Z") Instant hireDate) {

but when CodeGen generate the Java client code, it set date as OffsetDateTime. So to use Instant instead I use options typeMapping and importMapping to change Types. It work well for generated models classes but not for Api classes. Where type mapping work but not import mapping and the code does not compile.

output from mvn package

[ERROR] COMPILATION ERROR : 
[INFO] -------------------------------------------------------------
[ERROR] /home/hugo/IdeaProjects/perso/tut-rest/rest/src/main/java/com/test/generated/api/EmployeeControllerApi.java:[262,45] cannot find symbol
  symbol:   class Instant
  location: class com.test.generated.api.EmployeeControllerApi

And the compiled code Have the rigth type mapping

  public ResourcesEmployee searchUsingGET(Instant searchAfter) throws RestClientException

But Instant is not imported

Swagger-codegen version

Tried with swagger-codegen-maven-plugin version 2.4.7

Command line used for generation

I use the maven plugin to generate the code but this command line to the trick

java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate --library=resttemplate -i http://localhost:8080/v2/api-docs -l java --type-mappings OffsetDateTime=Instant --import-mappings java.time.OffsetDateTime=java.time.Instant -DdateLibrary=java8

Steps to reproduce

Create an API that use Swagger2
Create an GET endpoint that use java.time.Instant
run java -jar modules/swagger-codegen-cli/target/swagger-codegen-cli.jar generate --library=resttemplate -i http://localhost:8080/v2/api-docs -l java --type-mappings OffsetDateTime=Instant --import-mappings java.time.OffsetDateTime=java.time.Instant -DdateLibrary=java8

Suggest a fix/enhancement

I don't really know how to solve this now but I'm pretty sure it's around this line https://github.com/swagger-api/swagger-codegen/blob/83a3de0a970f0fd23cbc44ae87e0484aaaacd450/modules/swagger-codegen/src/main/java/io/swagger/codegen/DefaultGenerator.java#L989

if I print the values in AllImport the value specified in --import-mapping is missing

swagger-api / swagger-codegen