diff --git a/src/main/java/io/weaviate/client6/v1/api/collections/Vectors.java b/src/main/java/io/weaviate/client6/v1/api/collections/Vectors.java
index 2c5dacf4..b89cf7fc 100644
--- a/src/main/java/io/weaviate/client6/v1/api/collections/Vectors.java
+++ b/src/main/java/io/weaviate/client6/v1/api/collections/Vectors.java
@@ -186,7 +186,9 @@ public Vectors read(JsonReader in) throws IOException {
                 vector = float_1d.fromJsonTree(array);
               }
 
-              assert (vector instanceof float[]) || (vector instanceof float[][]) : "invalid vector type";
+              assert (vector instanceof float[]) || (vector instanceof float[][])
+                  : "invalid vector type " + vector.getClass();
+
               namedVectors.put(vectorName, vector);
             }
           }
diff --git a/src/main/java/io/weaviate/client6/v1/api/collections/aggregate/AggregateRequest.java b/src/main/java/io/weaviate/client6/v1/api/collections/aggregate/AggregateRequest.java
index 89e891cf..fa8290f6 100644
--- a/src/main/java/io/weaviate/client6/v1/api/collections/aggregate/AggregateRequest.java
+++ b/src/main/java/io/weaviate/client6/v1/api/collections/aggregate/AggregateRequest.java
@@ -4,8 +4,8 @@
 import java.util.HashMap;
 import java.util.Map;
 
-import io.weaviate.client6.v1.internal.DateUtil;
 import io.weaviate.client6.v1.api.collections.CollectionHandleDefaults;
+import io.weaviate.client6.v1.internal.DateUtil;
 import io.weaviate.client6.v1.internal.grpc.Rpc;
 import io.weaviate.client6.v1.internal.grpc.protocol.WeaviateGrpc.WeaviateBlockingStub;
 import io.weaviate.client6.v1.internal.grpc.protocol.WeaviateGrpc.WeaviateFutureStub;
@@ -79,7 +79,7 @@ static <T> Rpc<AggregateRequest, WeaviateProtoAggregate.AggregateRequest, Aggreg
           } else if (groupBy.hasBooleans()) {
             groupedBy = new GroupedBy<>(property, groupBy.getBooleans().getValuesList().toArray(Boolean[]::new));
           } else {
-            assert false : "(aggregate) branch not covered";
+            throw new IllegalArgumentException(property + " data type is not supported");
           }
 
           var properties = unmarshalAggregation(result.getAggregations());
@@ -148,7 +148,7 @@ private static Map<String, Object> unmarshalAggregation(WeaviateProtoAggregate.A
             metric.hasMode() ? metric.getMode() : null,
             metric.hasSum() ? metric.getSum() : null);
       } else {
-        assert false : "branch not covered";
+        throw new IllegalArgumentException(property + " data type is not supported");
       }
 
       if (value != null) {
diff --git a/src/main/java/io/weaviate/client6/v1/api/collections/pagination/AsyncPage.java b/src/main/java/io/weaviate/client6/v1/api/collections/pagination/AsyncPage.java
index baddef6f..691b8bad 100644
--- a/src/main/java/io/weaviate/client6/v1/api/collections/pagination/AsyncPage.java
+++ b/src/main/java/io/weaviate/client6/v1/api/collections/pagination/AsyncPage.java
@@ -61,7 +61,9 @@ public CompletableFuture<AsyncPage<PropertiesT>> fetchNextPage() {
           // If it is null after the first iteration it is
           // because we haven't requested Metadata.UUID, in which
           // case pagination will continue to run unbounded.
-          assert nextCursor != null : "page cursor is null";
+          if (nextCursor == null) {
+            throw new IllegalStateException("page cursor is null");
+          }
           return new AsyncPage<>(nextCursor, pageSize, fetch, nextPage);
         });
   }
diff --git a/src/main/java/io/weaviate/client6/v1/api/collections/pagination/CursorSpliterator.java b/src/main/java/io/weaviate/client6/v1/api/collections/pagination/CursorSpliterator.java
index 27132fc2..3b0335d8 100644
--- a/src/main/java/io/weaviate/client6/v1/api/collections/pagination/CursorSpliterator.java
+++ b/src/main/java/io/weaviate/client6/v1/api/collections/pagination/CursorSpliterator.java
@@ -45,7 +45,9 @@ public boolean tryAdvance(Consumer<? super WeaviateObject<PropertiesT, Object, Q
     // If it is null after the first iteration it is
     // because we haven't requested Metadata.UUID, in which
     // case pagination will continue to run unbounded.
-    assert cursor != null : "page cursor is null";
+    if (cursor == null) {
+      throw new IllegalStateException("page cursor is null");
+    }
 
     currentPage = nextPage.iterator();
     return tryAdvance(action);
diff --git a/src/main/java/io/weaviate/client6/v1/api/collections/query/QueryRequest.java b/src/main/java/io/weaviate/client6/v1/api/collections/query/QueryRequest.java
index cb9daa54..4cd09638 100644
--- a/src/main/java/io/weaviate/client6/v1/api/collections/query/QueryRequest.java
+++ b/src/main/java/io/weaviate/client6/v1/api/collections/query/QueryRequest.java
@@ -256,7 +256,7 @@ private static <T> void setProperty(String property, WeaviateProtoProperties.Val
         builder.setOffsetDateTimeArray(property, dates);
       }
     } else {
-      assert false : "(query) branch not covered";
+      throw new IllegalArgumentException(property + " data type is not supported");
     }
   }
 }
diff --git a/src/main/java/io/weaviate/client6/v1/internal/orm/PojoDescriptor.java b/src/main/java/io/weaviate/client6/v1/internal/orm/PojoDescriptor.java
index bcb1b470..d0a1f218 100644
--- a/src/main/java/io/weaviate/client6/v1/internal/orm/PojoDescriptor.java
+++ b/src/main/java/io/weaviate/client6/v1/internal/orm/PojoDescriptor.java
@@ -147,7 +147,7 @@ private ObjectBuilder<CollectionConfig> inspectClass(CollectionConfig.Builder b)
       }
 
       if (ctor == null) {
-        throw new IllegalArgumentException(type.getCanonicalName() + " fields are not supported");
+        throw new IllegalArgumentException(type.getCanonicalName() + " property is not supported");
       }
 
       assert ctor != null;
diff --git a/src/main/java/io/weaviate/client6/v1/internal/orm/PojoReader.java b/src/main/java/io/weaviate/client6/v1/internal/orm/PojoReader.java
index 82ccea5a..41ace15d 100644
--- a/src/main/java/io/weaviate/client6/v1/internal/orm/PojoReader.java
+++ b/src/main/java/io/weaviate/client6/v1/internal/orm/PojoReader.java
@@ -15,12 +15,15 @@ public Map<String, Object> readProperties() {
     var out = new HashMap<String, Object>();
     for (var field : properties.getClass().getDeclaredFields()) {
       var propertyName = PojoDescriptor.propertyName(field);
-      field.setAccessible(true);
-      try {
-        out.put(propertyName, field.get(properties));
-      } catch (IllegalAccessException e) {
-        assert e == null : e.getMessage();
+      if (field.trySetAccessible()) {
+        try {
+          out.put(propertyName, field.get(properties));
+        } catch (IllegalAccessException e) {
+          new RuntimeException("accessible flag set but access denied", e);
+        }
       }
+      // TODO: how do we handle the case where a property is not accessible?
+      // E.g. we weren't able to set `accessible` flag.
     }
     return out;
   }