Cannot insert null into database vb.net -

i have been trying insert null database every time getting failed. tried several codes nothing working. when tried code:

   if string.isnullorempty(textbox2.text)         textbox2.text = dbnull.value     else         textbox2.text = textbox2.text      end if 

it gives me error :

value of type 'system.dbnull' cannot converted 'string'. 

and when tried this:

    if not string.isnullorempty(textbox2.text) = true         textbox2 = system.dbnull.value     else         textbox2.text = textbox2.text     end if 

it gives me error:

  value of type 'system.dbnull' cannot converted 'system.windows.forms.textbox'. 

before these code have added validations in order make text box compulsory filled user.

this place getting error:

    dsnewrow.item("emp_name") = textbox1.text     dsnewrow.item("emp_age") = textbox2.text  'this place getting error'     dsnewrow.item("emp_gend") = combobox1.text     dsnewrow.item("emp_dob") = datetimepicker1.text     dsnewrow.item("emp_mstatus") = textbox4.text     dsnewrow.item("emp_qual") = richtextbox1.text     dsnewrow.item("emp_exp") = richtextbox2.text 

it shows:

 input string not in correct format.couldn't store <> in emp_age column.  expected type int32. 

the dbnull.value assigned datarow column using syntax (assuming, of course, emp_age column nullable)

dsnewrow.item("emp_age") =      if(string.isnullorwhitespace(textbox2.text), dbnull.value, textbox2.text) 

here, use if conditional operator set value of column dbnull.value or textbox2.text

however, there problem not visible. emp_age column requires integer value , shouldn't write in string. better check input value sure have valid integer value

dim age integer if int32.tryparse(textbox2.text, age)     dsnewrow.item("emp_age") = age else     dsnewrow.item("emp_age") = dbnull.value end if