TeamCity version: TeamCity 2018.2.4 (build 61678), effective release date 2018-12-06.

After adding a Connection to a TeamCity project for our Bitbucket Cloud account, using OAuth2, I get this "Unexpected Error", when trying to authorize (sign in).

Steps:

1. I click the Sign in to Bitbucket button (in TeamCity).
2. It pops up the Bitbucket OAuth page. This page asks me to grant certain access permissions to TeamCity.
3. I click the button to grant all permissions.
4. It redirects me back to TeamCity, which has an Unexpected Error page.

Error:

URL: /oauth/bitbucket/accessToken.html?action=completeAuthorization&projectId=_Root&code=hxLsGTGe5VY4fPtUAW&connectionId=PROJECT_EXT_2&callbackUrl=%2Foauth%2Fbitbucket%2Frepositories.html%3FprojectId%3D_Root%26connectionId%3DPROJECT_EXT_2%26tokenObtained%3Dtrue%26showMode%3DcreateProjectMenu

Unexpected Error

This was not supposed to happen. Please provide the error details to your TeamCity server maintainer.
If you maintain this TeamCity installation and the request seems legit please report this error to JetBrains.

Trace: java.io.IOException: Failed to get user profile
	at jetbrains.buildServer.serverSide.oauth.bitbucket.BitBucketAccessTokenController.getBitBucketUser(BitBucketAccessTokenController.java:226)
	at jetbrains.buildServer.serverSide.oauth.bitbucket.BitBucketAccessTokenController.lambda$doHandle$2(BitBucketAccessTokenController.java:147)
	at jetbrains.buildServer.util.HTTPRequestBuilder$ApacheClient43RequestHandler.doRequest(HTTPRequestBuilder.java:14)
	at jetbrains.buildServer.serverSide.oauth.bitbucket.BitBucketAccessTokenController.doHandle(BitBucketAccessTokenController.java:156)
	at jetbrains.buildServer.controllers.BaseController.handleRequestInternal(BaseController.java:114)
	at org.springframework.web.servlet.mvc.AbstractController.handleRequest(AbstractController.java:174)
	at jetbrains.buildServer.controllers.BaseController.handleRequest(BaseController.java:93)
	at org.springframework.web.servlet.mvc.SimpleControllerHandlerAdapter.handle(SimpleControllerHandlerAdapter.java:50)
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:967)
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:901)
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:970)
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:861)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:635)
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:846)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:742)
	at jetbrains.buildServer.maintenance.TeamCityDispatcherServlet.processedByMainServlet(TeamCityDispatcherServlet.java:22)
	at jetbrains.buildServer.maintenance.TeamCityDispatcherServlet.service(TeamCityDispatcherServlet.java:3)
	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:52)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at jetbrains.buildServer.web.jsp.JspPrecompilerFilter.doFilter(JspPrecompilerFilter.java:133)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at jetbrains.buildServer.web.DisableSessionIdFromUrlFilter.doFilter(DisableSessionIdFromUrlFilter.java:8)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at jetbrains.buildServer.web.UserIdProviderFilter.doFilter(UserIdProviderFilter.java:8)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at jetbrains.buildServer.web.NodeInfoHeaderFilter.doFilter(NodeInfoHeaderFilter.java:3)
	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.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:107)
	at jetbrains.buildServer.diagnostic.web.DiagnosticFilter.doFilter(DiagnosticFilter.java:54)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:112)
	at jetbrains.buildServer.web.DependencyParametersCalculationContextFilter.doFilter(DependencyParametersCalculationContextFilter.java:13)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:112)
	at jetbrains.buildServer.web.ContentSecurityPolicyFilter.doFilter(ContentSecurityPolicyFilter.java:3)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:112)
	at jetbrains.buildServer.web.CSRFFilter.doFilter(CSRFFilter.java:112)
	at org.springframework.web.filter.CompositeFilter$VirtualFilterChain.doFilter(CompositeFilter.java:112)
	at org.springframework.web.filter.CompositeFilter.doFilter(CompositeFilter.java:73)
	at jetbrains.buildServer.web.DelegatingFilter.doFilter(DelegatingFilter.java:61)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at jetbrains.buildServer.web.ResponseFragmentFilter.doFilter(ResponseFragmentFilter.java:5)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:493)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:342)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:800)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:806)
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1498)
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.lang.Thread.run(Thread.java:748)
Caused by: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 29 path $.error
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:221)
	at com.google.gson.Gson.fromJson(Gson.java:814)
	at com.google.gson.Gson.fromJson(Gson.java:779)
	at com.google.gson.Gson.fromJson(Gson.java:728)
	at com.google.gson.Gson.fromJson(Gson.java:700)
	at jetbrains.buildServer.serverSide.oauth.bitbucket.BitBucketAccessTokenController.lambda$getBitBucketUser$4(BitBucketAccessTokenController.java:202)
	at jetbrains.buildServer.util.HTTPRequestBuilder$ApacheClient43RequestHandler.doRequest(HTTPRequestBuilder.java:93)
	at jetbrains.buildServer.serverSide.oauth.bitbucket.BitBucketAccessTokenController.getBitBucketUser(BitBucketAccessTokenController.java:216)
	... 65 more
Caused by: java.lang.IllegalStateException: Expected a string but was BEGIN_OBJECT at line 1 column 29 path $.error
	at com.google.gson.stream.JsonReader.nextString(JsonReader.java:837)
	at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:360)
	at com.google.gson.internal.bind.TypeAdapters$13.read(TypeAdapters.java:348)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$1.read(ReflectiveTypeAdapterFactory.java:117)
	at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:217)
	... 72 more