diff --git a/sotopia/samplers/constraint_based_sampler.py b/sotopia/samplers/constraint_based_sampler.py
index 624520dcd..28f127a20 100644
--- a/sotopia/samplers/constraint_based_sampler.py
+++ b/sotopia/samplers/constraint_based_sampler.py
@@ -87,10 +87,16 @@ def sample(
         agents_which_fit_scenario: list[list[str]] = []
 
         if self.env_candidates is None:
-            self.env_candidates = EnvironmentProfile.all()
+            env_candidates = EnvironmentProfile.all()
+            if not env_candidates:
+                raise ValueError("No environment candidates available for sampling.")
+            self.env_candidates = env_candidates
 
         if self.agent_candidates is None:
-            self.agent_candidates = AgentProfile.all()
+            agent_candidates = AgentProfile.all()
+            if not agent_candidates:
+                raise ValueError("No agent candidates available for sampling.")
+            self.agent_candidates = agent_candidates
 
         agent_candidate_ids: set[str] | None = None
         if self.agent_candidates:
diff --git a/sotopia/samplers/uniform_sampler.py b/sotopia/samplers/uniform_sampler.py
index 22c89f3c3..bfb729f55 100644
--- a/sotopia/samplers/uniform_sampler.py
+++ b/sotopia/samplers/uniform_sampler.py
@@ -47,10 +47,16 @@ def sample(
         assert replacement, "Uniform sampling without replacement is not supported yet"
 
         if self.env_candidates is None:
-            self.env_candidates = EnvironmentProfile.all()
+            env_candidates = EnvironmentProfile.all()
+            if not env_candidates:
+                raise ValueError("No environment candidates available for sampling.")
+            self.env_candidates = env_candidates
 
         if self.agent_candidates is None:
-            self.agent_candidates = AgentProfile.all()
+            agent_candidates = AgentProfile.all()
+            if not agent_candidates:
+                raise ValueError("No agent candidates available for sampling.")
+            self.agent_candidates = agent_candidates
 
         for _ in range(size):
             env_profile = random.choice(self.env_candidates)