diff --git a/src/lib.rs b/src/lib.rs
index 6441e72..b4d5ec6 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -58,7 +58,10 @@ fn read_string(reader: &mut impl Read) -> io::Result<String> {
     let len = reader.read_u8()?;
     let mut buffer = vec![0; len as usize];
     reader.read_exact(&mut buffer)?;
-    Ok(String::from_utf8_lossy(&buffer).into_owned())
+    Ok(String::from_utf8_lossy(&buffer)
+        .replace('\0', "")
+        .replace('\u{FFFD}', "")
+        .to_string())
 }
 
 fn parse_column_type(type_str: &str) -> (ColumnType, Option<String>) {
@@ -90,19 +93,18 @@ fn parse_column_type(type_str: &str) -> (ColumnType, Option<String>) {
 
 fn read_column_data(reader: &mut impl Read, column_type: &ColumnType, rows: u64) -> io::Result<Vec<ColumnData>> {
     let mut data = Vec::with_capacity(rows as usize);
-    for i in 0..rows {
+    for _ in 0..rows {
         let value = match column_type {
             ColumnType::UInt64 => {
                 let val = reader.read_u64::<LittleEndian>()?;
-                // if i < 5 || i == rows - 1 {
-                //     println!("Row {}: {}", i, val);
-                // }
                 ColumnData::UInt64(val)
             },
             ColumnType::String => ColumnData::String(read_string(reader)?),
             ColumnType::UInt8 | ColumnType::Enum8 => ColumnData::UInt8(reader.read_u8()?),
             ColumnType::Int => ColumnData::Int(reader.read_i32::<LittleEndian>()?),
-            ColumnType::Unsupported(_) => ColumnData::Null,
+            ColumnType::Unsupported(type_name) => {
+                ColumnData::String(format!("<unsupported:{}>", type_name))
+            }
         };
         data.push(value);
     }
@@ -126,11 +128,9 @@ fn read_var_u64(reader: &mut impl Read) -> io::Result<u64> {
 }
 
 fn skip_block_header(reader: &mut BufReader<File>) -> io::Result<()> {
-    // Skip the marker
     let mut marker = [0u8; 4];
     reader.read_exact(&mut marker)?;
     
-    // Skip two strings (each prefixed with length)
     for _ in 0..2 {
         let str_len = reader.read_u8()? as u64;
         reader.seek_relative(str_len as i64)?;
@@ -140,14 +140,10 @@ fn skip_block_header(reader: &mut BufReader<File>) -> io::Result<()> {
 }
 
 fn read_native_format(reader: &mut BufReader<File>) -> io::Result<Vec<Column>> {
-    // Read number of columns
     let num_columns = read_var_u64(reader)?;
     let mut columns = Vec::new();
-
-    // Read block size
     let num_rows = read_var_u64(reader)?;
 
-    // Read column definitions and first block data
     for _ in 0..num_columns {
         let name = read_string(reader)?;
         let type_str = read_string(reader)?;        
@@ -156,13 +152,11 @@ fn read_native_format(reader: &mut BufReader<File>) -> io::Result<Vec<Column>> {
         columns.push(Column { name, type_: column_type, type_params, data });
     }
 
-    // Read subsequent blocks
     loop {
-        // Try to read number of columns for next block
-        let pos = reader.stream_position()?;
+        let _pos = reader.stream_position()?;
         let block_columns = match read_var_u64(reader) {
             Ok(cols) => cols,
-            Err(_) => break,  // End of file
+            Err(_) => break,
         };
 
         let block_rows = read_var_u64(reader)?;
@@ -171,13 +165,11 @@ fn read_native_format(reader: &mut BufReader<File>) -> io::Result<Vec<Column>> {
             break;
         }
 
-        // Skip column definitions for the block (they should match)
         for _ in 0..block_columns {
-            let _ = read_string(reader)?;  // column name
-            let _ = read_string(reader)?;  // column type
+            let _ = read_string(reader)?;
+            let _ = read_string(reader)?;
         }
 
-        // Read block data
         for col in &mut columns {
             let mut new_data = read_column_data(reader, &col.type_, block_rows)?;
             col.data.append(&mut new_data);
@@ -260,11 +252,16 @@ impl VTab for ClickHouseVTab {
                 let mut vector = output.flat_vector(col_idx);
 
                 match &column.type_ {
-                    ColumnType::String => {
+                    ColumnType::String | ColumnType::Unsupported(_) => {
                         for row in 0..batch_size {
                             let data_idx = (*init_data).current_row + row;
-                            if let ColumnData::String(s) = &column.data[data_idx] {
-                                vector.insert(row, s.as_str());
+                            match &column.data[data_idx] {
+                                ColumnData::String(s) => {
+                                    let cleaned = s.replace('\0', "")
+                                                 .replace('\u{FFFD}', "");
+                                    vector.insert(row, cleaned.as_str())
+                                },
+                                _ => vector.insert(row, "<invalid>"),
                             }
                         }
                     },
@@ -295,11 +292,6 @@ impl VTab for ClickHouseVTab {
                             }
                         }
                     },
-                    ColumnType::Unsupported(_) => {
-                        for row in 0..batch_size {
-                            vector.insert(row, "NULL");
-                        }
-                    },
                 }
             }
             (*init_data).current_row += batch_size;