diff --git a/src/main/java/millions/Share.java b/src/main/java/millions/Share.java
index afb3947..5db6738 100644
--- a/src/main/java/millions/Share.java
+++ b/src/main/java/millions/Share.java
@@ -11,6 +11,16 @@ public Share(Stock stock, BigDecimal quantity, BigDecimal purchasePrice) {
     this.stock = stock;
     this.quantity = quantity;
     this.purchasePrice = purchasePrice;
+
+    if (stock == null) {
+      throw new IllegalArgumentException("Stock cannot be null");
+    }
+    if (quantity == null) {
+      throw new IllegalArgumentException("Quantity cannot be null");
+    }
+    if (purchasePrice == null) {
+      throw new IllegalArgumentException("Purchase price cannot be null");
+    }
   }
 
   public Share(Stock stock, int quantity, BigDecimal purchasePrice) {