diff --git a/scm-webapp/src/main/java/sonia/scm/api/FallbackExceptionMapper.java b/scm-webapp/src/main/java/sonia/scm/api/FallbackExceptionMapper.java
new file mode 100644
index 0000000000..feb5341e2d
--- /dev/null
+++ b/scm-webapp/src/main/java/sonia/scm/api/FallbackExceptionMapper.java
@@ -0,0 +1,43 @@
+package sonia.scm.api;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+import org.slf4j.MDC;
+import sonia.scm.api.v2.resources.ErrorDto;
+import sonia.scm.api.v2.resources.ExceptionWithContextToErrorDtoMapper;
+import sonia.scm.web.VndMediaType;
+
+import javax.inject.Inject;
+import javax.ws.rs.core.Response;
+import javax.ws.rs.ext.ExceptionMapper;
+import javax.ws.rs.ext.Provider;
+import java.util.Collections;
+
+@Provider
+public class FallbackExceptionMapper implements ExceptionMapper<Exception> {
+
+  private static final Logger logger = LoggerFactory.getLogger(FallbackExceptionMapper.class);
+
+  private static final String ERROR_CODE = "CmR8GCJb31";
+
+  private final ExceptionWithContextToErrorDtoMapper mapper;
+
+  @Inject
+  public FallbackExceptionMapper(ExceptionWithContextToErrorDtoMapper mapper) {
+    this.mapper = mapper;
+  }
+
+  @Override
+  public Response toResponse(Exception exception) {
+    logger.debug("map {} to status code 500", exception);
+    ErrorDto errorDto = new ErrorDto();
+    errorDto.setMessage("internal server error");
+    errorDto.setContext(Collections.emptyList());
+    errorDto.setErrorCode(ERROR_CODE);
+    errorDto.setTransactionId(MDC.get("transaction_id"));
+    return Response.status(Response.Status.INTERNAL_SERVER_ERROR)
+      .entity(errorDto)
+      .type(VndMediaType.ERROR_TYPE)
+      .build();
+  }
+}
diff --git a/scm-webapp/src/main/java/sonia/scm/api/rest/ContextualExceptionMapper.java b/scm-webapp/src/main/java/sonia/scm/api/rest/ContextualExceptionMapper.java
index 43b8a38ccc..d8ab4033d1 100644
--- a/scm-webapp/src/main/java/sonia/scm/api/rest/ContextualExceptionMapper.java
+++ b/scm-webapp/src/main/java/sonia/scm/api/rest/ContextualExceptionMapper.java
@@ -13,7 +13,7 @@ public class ContextualExceptionMapper<E extends ExceptionWithContext> implement
 
   private static final Logger logger = LoggerFactory.getLogger(ContextualExceptionMapper.class);
 
-  private ExceptionWithContextToErrorDtoMapper mapper;
+  private final ExceptionWithContextToErrorDtoMapper mapper;
 
   private final Response.Status status;
   private final Class<E> type;
diff --git a/scm-webapp/src/main/java/sonia/scm/api/v2/resources/ErrorDto.java b/scm-webapp/src/main/java/sonia/scm/api/v2/resources/ErrorDto.java
index f0df654866..bd889d5de5 100644
--- a/scm-webapp/src/main/java/sonia/scm/api/v2/resources/ErrorDto.java
+++ b/scm-webapp/src/main/java/sonia/scm/api/v2/resources/ErrorDto.java
@@ -17,7 +17,7 @@ public class ErrorDto {
   private List<ContextEntry> context;
   private String message;
 
-  @XmlElement(name = "violation")
+  @JsonInclude(JsonInclude.Include.NON_NULL)
   @XmlElementWrapper(name = "violations")
   private List<ConstraintViolationDto> violations;