Fixed issue of formula calculation in application

src/main/java/net/gepafin/tendermanagement/dao/ApplicationDao.java

@@ -1792,10 +1792,14 @@ public class ApplicationDao {
         String expression = formula;
         for (String variable : variables) {
             Double value = variableValues.get(variable);
-            if (value != null) {
-                // Replace {variable} with its corresponding value in the formula
-                expression = expression.replace("{" + variable + "}", String.valueOf(value));
-            }
+            String placeholder = "{" + variable + "}";
+
+            // If value is null, use 0 instead
+            String replacement = String.valueOf(value != null ? value : 0);
+            expression = expression.replace(placeholder, replacement);
+        }
+        if (expression.matches(".*\\{.*\\}.*")) {
+            return 0;
         }
 
         // Step 4: Evaluate the mathematical expression