Player adding null and negative checks

src/main/java/millions/Player.java

@@ -15,13 +15,27 @@ public Player(String name, BigDecimal startingMoney) {
     this.money = startingMoney;
     this.portfolio = new Portfolio();
     this.transactionArchive = new TransactionArchive();
+
+    if (name == null || name.isBlank()) {
+      throw new IllegalArgumentException("Player name cannot be null or blank");
+    }
+
+    if (startingMoney == null || startingMoney.compareTo(BigDecimal.ZERO) < 0) {
+      throw new IllegalArgumentException("Starting money cannot be null or negative");
+    }
   }
 
   public void addMoney(BigDecimal amount) {
+    if (amount == null || amount.compareTo(BigDecimal.ZERO) < 0) {
+      throw new IllegalArgumentException("Amount cannot be null or negative");
+    }
     this.money = this.money.add(amount);
   }
 
   public void withdrawMoney(BigDecimal amount) {
+    if (amount == null || amount.compareTo(BigDecimal.ZERO) < 0) {
+      throw new IllegalArgumentException("Amount cannot be null or negative");
+    }
     this.money = this.money.subtract(amount);
   }