JsonMappingException if ResponseStatus == NO_CONTENT (204)

[Ichigo85]

Hi. I'm trying to make the migration to springdoc-openapi. After updating from 1.3.4 to 1.3.7 I have an error on java controller methods with annotation
@ResponseStatus(HttpStatus.NO_CONTENT).

Creating OpenApi json I receive this error

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["/api/v0_6/operation/doSomething"]->io.swagger.v3.oas.models.PathItem["post"]->io.swagger.v3.oas.models.Operation["responses"]->io.swagger.v3.oas.models.responses.ApiResponses["null"])

[bnasslahsen]

Hi @Ichigo85,

Could you please add a sample Hello Controller to reproduce your issue ?

Can you validate if you are having the same result with latest snaphot?

[Ichigo85]

Can you validate if you are having the same result with latest snaphot?

Unfortunately not, with 1.3.8 version configuration is not working anymore. I received an error

...
Caused by: java.lang.IllegalStateException: Failed to introspect Class [org.springdoc.webmvc.core.SpringDocWebMvcConfiguration] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@368239c8]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:477)
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:451)
	at org.springframework.core.type.StandardAnnotationMetadata.getAnnotatedMethods(StandardAnnotationMetadata.java:154)
	... 45 more
Caused by: java.lang.NoClassDefFoundError: org/springdoc/core/GenericParameterBuilder

Here is a sample HelloController. I sincerely not sure what is the issue that triggers this error on responseMap. I have a similar (but smaller) controller and everything works fine. This HelloController is not working either.

@OpenAPIDefinition(
        info = @Info(
                title = "Hello controller",
                description = "Test error",
                version = "v0.1"
        )
)
@RestController
@RequestMapping(path = "/api/v0_1",
        produces = MediaType.APPLICATION_JSON_UTF8_VALUE)
@ApiResponses(value = {
        @ApiResponse(responseCode = "400",
                description = StandardApiControllerV0_6.MESSAGE_400,
                content = @io.swagger.v3.oas.annotations.media.Content(mediaType = MediaType.APPLICATION_JSON_UTF8_VALUE,
                        schema = @Schema(implementation = ResponseError.class))
        ),
        @ApiResponse(responseCode = "401",
                description = StandardApiControllerV0_6.MESSAGE_401,
                content = @io.swagger.v3.oas.annotations.media.Content(mediaType = MediaType.APPLICATION_JSON_UTF8_VALUE,
                        schema = @Schema(implementation = OAuth2ResponseError.class))
        ),
        @ApiResponse(responseCode = "403",
                description = StandardApiControllerV0_6.MESSAGE_403,
                content = @io.swagger.v3.oas.annotations.media.Content(mediaType = MediaType.APPLICATION_JSON_UTF8_VALUE,
                        schema = @Schema(implementation = ResponseError.class))
        )
})
public class HelloController {

        @Operation(operationId="getSomething",
                summary="Find Something by various search parameters.",
                tags="Something",
                responses = {
                        @ApiResponse(responseCode = "200",
                                description = MESSAGE_200)
                })
        @RequestMapping(path = "something", method = { RequestMethod.GET })
        public String getSomething() {
                return "something";
        }
}

and this is the error:

2020-05-04 16:50:03.988 [main] INFO  org.springdoc.api.AbstractOpenApiResource - Init duration for springdoc-openapi is: 329 ms
2020-05-04 16:50:04.014 [main] ERROR org.shared.orchestica.btl.controller.GlobalControllerExceptionHandler - An error occured during call /swagger/api-docs
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["/api/v0_1/something"]->io.swagger.v3.oas.models.PathItem["get"]->io.swagger.v3.oas.models.Operation["responses"]->io.swagger.v3.oas.models.responses.ApiResponses["null"])
	at com.fasterxml.jackson.databind.JsonMappingException.from(JsonMappingException.java:285)
	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:721)
	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:721)
	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:721)
	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:4094)
	at com.fasterxml.jackson.databind.ObjectMapper.writeValueAsString(ObjectMapper.java:3404)
	at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:110)
	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)

[bnasslahsen]

Might be duplicate of #630.
Unable to reproduce with the sample code provided.

Can be valdated with v1.3.8 released today.
The ticket can be reopened, if the relevant information to reproduce the issue are provided.