BAEL-2499 - Write to CSV in Java

Closes #15250

Adding a null check.

core-java-modules/core-java-io-conversions-2/src/main/java/com/baeldung/csv/WriteCsvFileExample.java

@@ -12,6 +12,10 @@ public class WriteCsvFileExample {
     }
 
     public String escapeSpecialCharacters(String data) {
+        if (data == null) {
+            throw new IllegalArgumentException("Input data cannot be null");
+        }
+        
         String escapedData = data.replaceAll("\\R", " ");
         if (data.contains(",") || data.contains("\"") || data.contains("'")) {
             data = data.replace("\"", "\"\"");