spring-data-rest: repositories with void methods causing NullPointerException since SpringDoc 1.5.6 until the current 1.5.9

[baromojm]

Describe the bug
Swagger UI was working fine in my project until 1.5.5 (included), but since 1.5.6 (up to latest current version 1.5.9) it's throwing a NullPointerException when loading http://localhost:8080/swagger-ui.html. Stack trace follows:

java.lang.NullPointerException: null
        at org.springdoc.data.rest.utils.SpringDocDataRestUtils.buildTextUriContent(SpringDocDataRestUtils.java:417)
        at org.springdoc.data.rest.core.DataRestResponseService.buildSearchResponse(DataRestResponseService.java:121)
        at org.springdoc.data.rest.core.DataRestOperationService.buildSearchOperation(DataRestOperationService.java:230)
        at org.springdoc.data.rest.core.DataRestOperationService.buildOperation(DataRestOperationService.java:133)
        at org.springdoc.data.rest.core.DataRestRouterOperationService.buildRouterOperation(DataRestRouterOperationService.java:288)
        at org.springdoc.data.rest.core.DataRestRouterOperationService.buildRouterOperation(DataRestRouterOperationService.java:227)
        at org.springdoc.data.rest.core.DataRestRouterOperationService.buildRouterOperationList(DataRestRouterOperationService.java:193)
        at org.springdoc.data.rest.core.DataRestRouterOperationService.buildSearchRouterOperationList(DataRestRouterOperationService.java:148)
        at org.springdoc.data.rest.SpringRepositoryRestResourceProvider.lambda$findSearchControllers$17(SpringRepositoryRestResourceProvider.java:366)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.accept(ForEachOps.java:183)
        at java.base/java.util.stream.ReferencePipeline$2$1.accept(ReferencePipeline.java:177)
        at java.base/java.util.HashMap$ValueSpliterator.forEachRemaining(HashMap.java:1675)
        at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)
        at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)
        at java.base/java.util.stream.ForEachOps$ForEachOp.evaluateSequential(ForEachOps.java:150)
        at java.base/java.util.stream.ForEachOps$ForEachOp$OfRef.evaluateSequential(ForEachOps.java:173)
        at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
        at java.base/java.util.stream.ReferencePipeline.forEach(ReferencePipeline.java:497)
        at org.springdoc.data.rest.SpringRepositoryRestResourceProvider.findSearchControllers(SpringRepositoryRestResourceProvider.java:366)
        at org.springdoc.data.rest.SpringRepositoryRestResourceProvider.findSearchResourceMappings(SpringRepositoryRestResourceProvider.java:345)
        at org.springdoc.data.rest.SpringRepositoryRestResourceProvider.getRouterOperations(SpringRepositoryRestResourceProvider.java:249)
        at org.springdoc.webmvc.api.OpenApiResource.getPaths(OpenApiResource.java:203)
        at org.springdoc.api.AbstractOpenApiResource.getOpenApi(AbstractOpenApiResource.java:287)
        at org.springdoc.webmvc.api.OpenApiResource.openapiJson(OpenApiResource.java:176)
        at org.springdoc.webmvc.api.OpenApiWebMvcResource.openapiJson(OpenApiWebMvcResource.java:116)
        at org.springdoc.webmvc.api.MultipleOpenApiWebMvcResource.openapiJson(MultipleOpenApiWebMvcResource.java:93)
        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:197)
        at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:141)
        at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:106)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:894)
        at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)
        at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)
        at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1063)
        at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)
        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:626)
        at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:733)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        at org.springframework.security.web.FilterChainProxy.doFilterInternal(FilterChainProxy.java:204)
        at org.springframework.security.web.FilterChainProxy.doFilter(FilterChainProxy.java:183)
        at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:358)
        at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:271)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        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:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        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:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        at org.springframework.boot.actuate.metrics.web.servlet.WebMvcMetricsFilter.doFilterInternal(WebMvcMetricsFilter.java:96)
        at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:119)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        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:189)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97)
        at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:542)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:143)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:357)
        at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:374)
        at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
        at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:893)
        at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1707)
        at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
        at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
        at java.base/java.util.concurrent.ThreadPoolExecutor$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)

To Reproduce
Spring Boot: 2.5.0 (issue also exists with 2.4.x)
springdoc-openapi-ui: 1.5.9 (issue also exists in all versions since 1.5.6 until 1.5.9)
springdoc-openapi-data-rest: 1.5.9
springdoc-openapi-security: 1.5.9

SpringdocConfig.java

@OpenAPIDefinition
@Configuration
public class SpringdocConfig {

  /**
   * Definition: app.
   * 
   * @return -
   */
  @Bean
  public GroupedOpenApi appOpenApi() {
    String[] packagesToScan = { "edu.cou.myapp.controller" };
    String[] pathsToMatch = { "/rest/**" };
    String[] pathsToExclude = { "/rest/caches/**", "/rest/export/**", "/rest/merida/**" };
    return GroupedOpenApi.builder().group("app").packagesToScan(packagesToScan).pathsToMatch(
        pathsToMatch).pathsToExclude(pathsToExclude).build();
  }

  /**
   * Definition: export.
   * 
   * @return -
   */
  @Bean
  public GroupedOpenApi exportOpenApi() {
    String[] paths = { "/rest/export/**" };
    return GroupedOpenApi.builder().group("export").pathsToMatch(paths).build();
  }

  /**
   * Definition: misc.
   * 
   * @return -
   */
  @Bean
  public GroupedOpenApi miscOpenApi() {
    String[] paths = { "/*", "/rest/caches/**", "/rest/merida/**", "/rest/tech/**" }; //NOSONAR
    return GroupedOpenApi.builder().group("misc").pathsToMatch(paths).build();
  }

  /**
   * OpenAPI Swagger-UI configuration.<br>
   * http://localhost:8080/swagger-ui.html<br>
   * http://localhost:8080/v3/api-docs<br>
   * 
   * @return -
   */
  @Bean
  public OpenAPI customOpenAPI() {
    final var locUrl = "http://localhost:8080";
    final var devUrl = "https://myapp-dev.cou.edu/myapp_back";
    final var testUrl = "https://myapp-test.cou.edu/myapp_back";
    final var preUrl = "https://myapp-pre.cou.edu/myapp_back";
    final var proUrl = "https://myapp.cou.edu/myapp_back";
    return new OpenAPI().addServersItem(new Server().url(locUrl)).addServersItem(new Server().url(
        devUrl)).addServersItem(new Server().url(testUrl)).addServersItem(new Server().url(preUrl))
        .addServersItem(new Server().url(proUrl)).info(new Info().title("MYAPP").description(
            "Whatever."))
        .components(new Components().addSecuritySchemes("bearer-key", new SecurityScheme().type(
            SecurityScheme.Type.HTTP).scheme("bearer")));
  }

}

Expected behavior
When loading http://localhost:8080/swagger-ui.html it shouldn't throw the NullPointerException.
Note: it worked fine until SpringDoc 1.5.5 (it fails with all version since 1.5.6 until the current 1.5.9)

Screenshots

Additional context
Project has Spring Data REST enabled.

[bnasslahsen]

@baromojm,

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

• Please make sure you provide a Minimal, Reproducible Example - with HelloController that reproduces the problem.

[baromojm]

Hello:
I've been able to reproduce the issue without any controller, only with Spring Data REST enabled.

Here is the project that allows to reproduce the issue:
springdoc-issue1171.zip

http://localhost:8080/swagger-ui.html

-fails to load with springdoc 1.5.9 (current latest release)
-it works fine with springdoc 1.5.5

Thank you,

[bnasslahsen]

@baromojm,

This should be fixed.
You can validate it using the latest snapshot.

[baromojm]

Verified successfully with snapshot 1.5.10-20210525.193947-2

Thank you,