diff --git a/src/panel/linear_composite.rs b/src/panel/linear_composite.rs
index 6198ce1..728b933 100644
--- a/src/panel/linear_composite.rs
+++ b/src/panel/linear_composite.rs
@@ -1,13 +1,42 @@
-use crate::utils::misc::*;
 use crate::utils::qdf::check_quantamental_dataframe;
 use crate::utils::qdf::pivots::*;
 use crate::utils::qdf::reduce_df::*;
-use chrono::NaiveDate;
-use ndarray::Data;
-use ndarray::{s, Array, Array1, Zip};
 use polars::prelude::*;
-use polars::series::Series; // Series struct
 use std::collections::HashMap;
+const TOLERANCE: f64 = 1e-8;
+
+fn _norm_apply_nan_mask(
+    weights_dfw: &DataFrame,
+    nan_mask_dfw: &DataFrame,
+) -> Result<DataFrame, PolarsError> {
+    let mut norm_dfw = DataFrame::new(vec![])?;
+    for col in weights_dfw.get_column_names().clone() {
+        let weight_col = weights_dfw.column(col)?;
+        let nan_mask_col = nan_mask_dfw.column(col)?;
+        let nan_mask_series = (!(nan_mask_col.bool()?)).into_column();
+        let float_col = nan_mask_series.cast(&DataType::Float64)?;
+        let float_series = (weight_col * &float_col)?;
+        let sum = float_series.f64()?.sum().unwrap();
+        if sum < TOLERANCE {
+            // get the sum of the nan_mask_series
+            let nan_mask_sum = nan_mask_series
+                .cast(&DataType::Float64)?
+                .f64()?
+                .sum()
+                .unwrap();
+            // if the sum of the nan_mask_series is close to the len of the series, then ok
+            let weight_sum = weight_col.f64()?.sum().unwrap();
+            let ratio = (nan_mask_sum - weight_col.len() as f64).abs() / weight_col.len() as f64;
+            assert!(
+                ratio < TOLERANCE,
+                "The sum of the updated series is zero: {:?} w ratio: {:?} and the weights summing to: {:?}",
+                sum, nan_mask_sum, weight_sum
+            );
+        }
+        norm_dfw.with_column(float_series)?;
+    }
+    Ok(norm_dfw)
+}
 
 fn normalize_weights_with_nan_mask(
     weights_dfw: DataFrame,
@@ -23,35 +52,14 @@ fn normalize_weights_with_nan_mask(
         "The columns in weights_dfw and nan_mask_dfw do not match."
     );
 
-    let col_names = weights_dfw.get_column_names();
-
-    // clone weights_dfw
-    let mut norm_dfw = DataFrame::new(vec![])?;
-    // Iterate over each column in the DataFrame, and apply the nan mask
-    for col in col_names.clone() {
-        let weight_series = weights_dfw.column(col)?;
-        let nan_mask_series = nan_mask_dfw.column(col)?;
-
-        // Replace values in `weight_series` with nulls where `nan_mask_series` is true
-        let updated_series = weight_series.zip_with(
-            nan_mask_series.bool()?,
-            &Series::full_null(
-                col.to_string().into(),
-                weight_series.len(),
-                weight_series.dtype(),
-            )
-            .into_column(),
-        )?;
-
-        // Update the column in the new DataFrame
-        norm_dfw.with_column(updated_series)?;
-    }
+    let mut norm_dfw = _norm_apply_nan_mask(&weights_dfw, &nan_mask_dfw)?;
 
     let sums_of_rows = norm_dfw
         .sum_horizontal(polars::frame::NullStrategy::Ignore)?
         .unwrap()
         .into_column();
-    for col in col_names {
+
+    for col in weights_dfw.get_column_names() {
         let weight_series = norm_dfw.column(col)?;
         let divided_series = weight_series.divide(&sums_of_rows)?;
         let normalized_series = divided_series.as_series().unwrap().clone();