java not running inside tool process

import org.joget.apps.form.model.FormData;
import org.joget.apps.form.service.FormService;
import org.joget.commons.util.LogUtil;

import java.util.Arrays;
import java.util.List;
import java.util.Map;

public class MultiSelectHandler {

    public void handleMultiSelectField(FormData formData, FormService formService) {
        // Get the multi-select field value from form data
        String multiSelectFieldName = "approversList";
        String fieldValue = formData.getFieldValue(multiSelectFieldName);
        
        if (fieldValue != null && !fieldValue.isEmpty()) {
            // Split the field value by semicolons to get a list of selected values
            List<String> selectedValues = Arrays.asList(fieldValue.split(";"));
            
            if (!selectedValues.isEmpty()) {
                // Get the first selected value
                String firstSelectedValue = selectedValues.get(0);
                
                // Store or use the first selected value as needed
                // For example, set it as a new value in the form data
                formData.getFieldValues().put("firstSelectedApprover", firstSelectedValue);
                
                // Optionally, log or further process the firstSelectedValue
                LogUtil.info(MultiSelectHandler.class.getName(), "First Selected Approver: " + firstSelectedValue);
            } else {
                LogUtil.info(MultiSelectHandler.class.getName(), "No values found after splitting.");
            }
        } else {
            LogUtil.info(MultiSelectHandler.class.getName(), "No values found in approversList.");
        }
    }
}

i put this java code inside tool process but it is not working, what is the reason ? 

note: the firstSelectedValue  is a process variable like approversList(come from multiselected box, multiple values),  i want to store inside  firstSelectedValue the first approver from approversList, the firstSelectedValue i have initialized it inside the from and give it a default value, so i want to save the first approver inside this variable as the code show but the code is not running why ? is there any library i should install or something ?