diff --git a/datastew/repository/weaviate.py b/datastew/repository/weaviate.py
index 70c1ea8..312bd92 100644
--- a/datastew/repository/weaviate.py
+++ b/datastew/repository/weaviate.py
@@ -459,7 +459,11 @@ def _sentence_embedder_exists(self, name: str) -> bool:
                 "operator": "Equal",
                 "valueText": name
             }).do()
-            return len(result["data"]["Get"]["Mapping"]) > 0
+            result_data = result["data"]["Get"]["Mapping"]
+            if result_data is not None:
+                return len(result_data) > 0
+            else:
+                return False
         except Exception as e:
             raise RuntimeError(f"Failed to check if sentence embedder exists: {e}")
 
@@ -470,7 +474,11 @@ def _terminology_exists(self, name: str) -> bool:
                 "operator": "Equal",
                 "valueText": name
             }).do()
-            return len(result["data"]["Get"]["Terminology"]) > 0
+            result_data = result["data"]["Get"]["Terminology"]
+            if result_data is not None:
+                return len(result_data) > 0
+            else:
+                return False
         except Exception as e:
             raise RuntimeError(f"Failed to check if terminology exists: {e}")
 
@@ -481,7 +489,11 @@ def _concept_exists(self, concept_id: str) -> bool:
                 "operator": "Equal",
                 "valueText": concept_id
             }).do()
-            return len(result["data"]["Get"]["Concept"]) > 0
+            result_data = result["data"]["Get"]["Concept"]
+            if result_data is not None:
+                return len(result_data) > 0
+            else:
+                return False
         except Exception as e:
             raise RuntimeError(f"Failed to check if concept exists: {e}")
 
@@ -491,6 +503,10 @@ def _mapping_exists(self, embedding) -> bool:
                 "vector": embedding,
                 "distance": float(0)  # Ensure distance is explicitly casted to float
             }).do()
-            return len(result["data"]["Get"]["Mapping"]) > 0
+            result_data = result["data"]["Get"]["Mapping"]
+            if result_data is not None:
+                return len(result_data) > 0
+            else:
+                return False
         except Exception as e:
             raise RuntimeError(f"Failed to check if mapping exists: {e}")