diff --git a/CHANGELOG.md b/CHANGELOG.md
index d46bc40..60f6d44 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,10 @@
 
 - Changed how survey version ID is generated, to use a shorter format (YY-MM-counter).
 
+### Fixed
+
+- `HasParticipantStateWithCondition` should handle case without condition as well. (When condition is nil)
+
 ## [v0.14.0]
 
 ### Added
diff --git a/pkg/grpc/service/studyinfo_endpoints.go b/pkg/grpc/service/studyinfo_endpoints.go
index 20ef0b2..b181581 100644
--- a/pkg/grpc/service/studyinfo_endpoints.go
+++ b/pkg/grpc/service/studyinfo_endpoints.go
@@ -115,7 +115,13 @@ func (s *studyServiceServer) HasParticipantStateWithCondition(ctx context.Contex
 		}
 
 		cond := types.ExpressionArgFromAPI(req.Condition)
-		if cond.IsExpression() {
+		if cond == nil {
+			return &api.ServiceStatus{
+				Version: apiVersion,
+				Status:  api.ServiceStatus_NORMAL,
+				Msg:     "participant found in study",
+			}, nil
+		} else if cond.IsExpression() {
 			evalCtx := studyengine.EvalContext{
 				ParticipantState: pState,
 			}