JsonMappingException on UI render

[jasonab]

Using version 1.3.6

Describe the bug
When trying to render /swagger-ui.html, receive the following error:
There was an unexpected error (type=Internal Server Error, status=500).
com.fasterxml.jackson.databind.JsonMappingException: Null key for a Map not allowed in JSON (use a converting NullKeySerializer?) (through reference chain: io.swagger.v3.oas.models.OpenAPI["paths"]->io.swagger.v3.oas.models.Paths["/keywordGroups/{groupName}"]->io.swagger.v3.oas.models.PathItem["get"]->io.swagger.v3.oas.models.Operation["responses"]->io.swagger.v3.oas.models.responses.ApiResponses["null"])

Expected behavior
Page would render Swagger documentation

I've removed all Swagger annotations from the code in question, leaving only Spring REST-oriented annotations, but cannot seem to get past this error. The method in question returns a ResponseEntity object, if that might matter.

I've also tried adding a full set of @operation + @ApiResponse objects, but it does not get rid of this error.

[bierchitekt]

Same issue here when upgrading from 1.3.4 to 1.3.6

[bnasslahsen]

@jasonab and @abadurczyk,

If you are reporting a bug, please help to speed up problem diagnosis by providing as much information as possible:

• Provide with a sample code (HelloController) or Test that reproduces the problem

[vicentesd93]

Same issue here when upgrading from 1.3.1 to 1.3.6

Null key for a Map not allowed in JSON (use a converting NullKeySerializer?) (through reference chain: io.swagger.v3.oas.models.OpenAPI["paths"]->io.swagger.v3.oas.models.Paths["/"]->io.swagger.v3.oas.models.PathItem["get"]->io.swagger.v3.oas.models.Operation["responses"]->io.swagger.v3.oas.models.responses.ApiResponses["null"])

[bnasslahsen]

@vicentesd93,

Is it the same issue with v1.3.7, which integrates some enhancements?
If its still the case, can you please provide more information about your context:

• Provide with a sample code (HelloController) or Test that reproduces the problem

[bnasslahsen]

This ticket will be closed, and there is no need to reopen a new ticket for the same issue.
You can add your comments if needed and we will follow it.

[vicentesd93]

@bnasslahsen

Yes we tested it and it plays.

My example:

import io.swagger.v3.oas.annotations.OpenAPIDefinition;
import io.swagger.v3.oas.annotations.Operation;
import io.swagger.v3.oas.annotations.Parameter;
import io.swagger.v3.oas.annotations.enums.ParameterIn;
import io.swagger.v3.oas.annotations.enums.ParameterStyle;
import io.swagger.v3.oas.annotations.info.Info;
import io.swagger.v3.oas.annotations.media.ArraySchema;
import io.swagger.v3.oas.annotations.media.Content;
import io.swagger.v3.oas.annotations.media.Schema;
import io.swagger.v3.oas.annotations.responses.ApiResponse;
import io.swagger.v3.oas.annotations.responses.ApiResponses;
import io.swagger.v3.oas.annotations.tags.Tag;

@Controller
@RequestMapping("/api")
@OpenAPIDefinition(info = @Info(title = "API Examples", version = "1.0"), tags = @Tag(name = "Operations"))
public interface IExamplesApi {

@Operation(operationId = "getExample", description = "Get examples", tags = {
			"Operations", })
	@ApiResponses(value = {
			@ApiResponse(responseCode = "200", description = "List of examples.", content = @Content(mediaType = MediaType.APPLICATION_JSON_VALUE, array = @ArraySchema(schema = @Schema(implementation = Examples.class)))),
			@ApiResponse(responseCode = "400", description = "Bad Request", content = @Content(mediaType = MediaType.APPLICATION_JSON_VALUE, schema = @Schema(implementation = Error.class))) })
	@RequestMapping(value = "/examples", produces = {
			MediaType.APPLICATION_JSON_VALUE }, method = RequestMethod.GET)
	ResponseEntity<List<Examples>> getExample(
			@Parameter(description = "user id", required = true, in = ParameterIn.PATH, style = ParameterStyle.SIMPLE, schema = @Schema(type = "number")) @PathVariable("userid") BigDecimal userid);

Thanks for the reply.

[bnasslahsen]

@jasonab,

Your issue is unable to reproduce...

If you are reporting a bug, please help to speed up problem diagnosis by providing as much information as possible: As mentionned before,

• Provide with a sample code (HelloController) or Test that reproduces the problem

[bierchitekt]

Version 1.3.7 does not fix it.

How to reproduce:
application.yml

springdoc:
  pathsToMatch: /v1/**

Controller:

@RestController
@RequestMapping("/v1")
public class FooController {
    @PostMapping("foo")
    public String create(@RequestBody String foo) {
        return "foo";
    }
}

Errorhandler:

@ControllerAdvice(assignableTypes = FooController.class)
public class FooErrorHandler {

    @ExceptionHandler
    public ResponseEntity<String> storeAssignmentPublishingError(Exception e) {
        return new ResponseEntity<>("foo", HttpStatus.INTERNAL_SERVER_ERROR);
    }
}

Exception:

ERROR o.a.c.c.C.[.[.[.[dispatcherServlet].log - Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception com.fasterxml.jackson.databind.JsonMappingException: Null key for a Map not allowed in JSON (use a converting NullKeySerializer?) (through reference chain: io.swagger.v3.oas.models.OpenAPI["paths"]->io.swagger.v3.oas.models.Paths["/v1/foo"]->io.swagger.v3.oas.models.PathItem["post"]->io.swagger.v3.oas.models.Operation["responses"]->io.swagger.v3.oas.models.responses.ApiResponses["null"]) at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:288) at com.fasterxml.jackson.databind.SerializerProvider.mappingException(SerializerProvider.java:1251) at com.fasterxml.jackson.databind.SerializerProvider.reportMappingProblem(SerializerProvider.java:1145) at com.fasterxml.jackson.databind.ser.impl.FailingSerializer.serialize(FailingSerializer.java:35) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serializeOptionalFields(MapSerializer.java:781) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:639) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:33) at com.fasterxml.jackson.databind.SerializerProvider.defaultSerializeValue(SerializerProvider.java:1033) at io.swagger.v3.core.jackson.ApiResponsesSerializer.serialize(ApiResponsesSerializer.java:35) at io.swagger.v3.core.jackson.ApiResponsesSerializer.serialize(ApiResponsesSerializer.java:11) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serializeOptionalFields(MapSerializer.java:782) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:639) at com.fasterxml.jackson.databind.ser.std.MapSerializer.serialize(MapSerializer.java:33) at com.fasterxml.jackson.databind.SerializerProvider.defaultSerializeValue(SerializerProvider.java:1033) at io.swagger.v3.core.jackson.PathsSerializer.serialize(PathsSerializer.java:35) at io.swagger.v3.core.jackson.PathsSerializer.serialize(PathsSerializer.java:11) at com.fasterxml.jackson.databind.ser.BeanPropertyWriter.serializeAsField(BeanPropertyWriter.java:727) at com.fasterxml.jackson.databind.ser.std.BeanSerializerBase.serializeFields(BeanSerializerBase.java:722) at com.fasterxml.jackson.databind.ser.BeanSerializer.serialize(BeanSerializer.java:166) at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider._serialize(DefaultSerializerProvider.java:480) at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:319) at com.fasterxml.jackson.databind.ObjectMapper._configAndWriteValue(ObjectMapper.java:4110) at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3413) at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:110) at org.springdoc.webmvc.api.MultipleOpenApiResource.openapiJson(MultipleOpenApiResource.java:128) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.base/java.lang.reflect.Method.invoke(Method.java:566) at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:190) at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:138) at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:105) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:879) at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:793) at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1040) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:943) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:898) at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:109) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:373) at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:868) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1594) at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128) at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.base/java.lang.Thread.run(Thread.java:834)

I hope you can fix it with these infos and thanks for your help :)

[bnasslahsen]

@jasonab,

The cause is that on the exception handler there is no @ResponseStatus.
The better solution is to add in order to display it in the swagger documentation.

@ControllerAdvice(assignableTypes = HelloController.class)
public class FooErrorHandler {

	@ExceptionHandler
	@ResponseStatus(HttpStatus.INTERNAL_SERVER_ERROR)
	public ResponseEntity<String> storeAssignmentPublishingError(Exception e) {
		return new ResponseEntity<>("foo", HttpStatus.INTERNAL_SERVER_ERROR);
	}
}

Anyway, the fix is now added to master, to ignore the ExceptionHandler if ResponseStatus is absent.