public void createTimeSheet() {
        errorMsg = '';
        TimeSheet__c newTimeSheet = new TimeSheet__c(
            Date__c = date.valueOf(newTimeSheetDate),
            Status__c = 'New',
            Employee__c = [SELECT Id FROM Employee__c WHERE Name=:EmployeeName].Id
        );
        try {
            insert newTimeSheet;
        //catching the DML exceptions first
        } catch(DmlException e) {
            errorMsg = e.getDmlMessage(0);
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,errorMsg));
        //catching all other exceptions
        } catch(Exception e) {
            errorMsg = e.getMessage();
            ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,errorMsg));
        }
}

public static testMethod void createTimeSheetNullPointerFail_test() {
        init();

        cont.EmployeeName = testEmployeeName;
        cont.tslist = testTsList;

        test.startTest();
            cont.createTimeSheet();
        test.stopTest();
        System.assert(cont.errorMsg.contains('System.NullPointerException: Attempt to de-reference a null object'), cont.errorMsg);
    }

try {
    Date.valueOf((String) null);
} catch (Exception e) {
    System.debug('>>> ' + e.getMessage());
}

public void createTimeSheet() {
    errorMsg = '';
    List<Employee__c> foundEmployees = [SELECT Id FROM Employee__c WHERE Name=:EmployeeName];
    if (foundEmployees.size() > 0) {
        TimeSheet__c newTimeSheet = new TimeSheet__c(
             Date__c = date.valueOf(newTimeSheetDate),
             Status__c = 'New',
            Employee__c = foundEmployees[0].Id
        );
    }
    else {
      // handle scenario here where the employee wasn't found, show error on page possibly
      // also consider adding else if scenario if more than 1 employee is found that matches the name
    }
    // TODO evaluate if try/catches are still needed
    try {
        insert newTimeSheet;
    //catching the DML exceptions first
    } catch(DmlException e) {
        errorMsg = e.getDmlMessage(0);
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,errorMsg));
    //catching all other exceptions
    } catch(Exception e) {
        errorMsg = e.getMessage();
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,errorMsg));
    }