Bug Report Checklist

• Have you provided a full/minimal spec to reproduce the issue?
• Have you validated the input using an OpenAPI validator (example)?
• What's the version of OpenAPI Generator used?
• Have you search for related issues/PRs?
• What's the actual output vs expected output?
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Description

When I use the optional configuration unhandledException=true in combination with skipDefaultInterface=true the exception is not thrown in the interface.

openapi-generator version

4.2.0

Actual output vs expected output

Actual

Mono<ResponseEntity<TransactionModel>> updateTransaction(@ApiParam(value = "",required=true) @PathVariable("transactionId") Long transactionId,@ApiParam(value = "the transaction to be updated"  )  @Valid @RequestBody Mono<TransactionModel> transactionModel, ServerWebExchange exchange);

Expected

Mono<ResponseEntity<TransactionModel>> updateTransaction(@ApiParam(value = "",required=true) @PathVariable("transactionId") Long transactionId,@ApiParam(value = "the transaction to be updated"  )  @Valid @RequestBody Mono<TransactionModel> transactionModel, ServerWebExchange exchange) throws Exception;

Command line used for generation

<generatorName>spring</generatorName>
<modelNameSuffix>Model</modelNameSuffix>
<configOptions>
  <sourceFolder>src/gen/java/main</sourceFolder>
  <unhandledException>true</unhandledException>
  <interfaceOnly>true</interfaceOnly>
  <skipDefaultInterface>true</skipDefaultInterface>
  <java8>true</java8>
  <dateLibrary>java8</dateLibrary>
  <booleanGetterPrefix>is</booleanGetterPrefix>
  <reactive>true</reactive>
</configOptions>