title: antd 4: setting a default value for Select with defaultValue, can't use initialValue
body: <p>In our rather complex form we have a dynamic form field (similar to the example in the antd documentation, except using a Select field). We use initialValue to feed our Form data from the database, now we want to have our Select fields, which are added dynamically, to have a default value.</p>
  
  <p>The problem exists in the fact that it isn't possible to add an initialValue to fields that haven't rendered yet + form doesn't know how many dynamic Select fields will be added.</p>
  
  <p>So instinctively I resorted to the defaultValue prop on the Select box, which in my eyes should just work, but it doesn't. (in antd 4 there is no fieldDescriptor with a defaultValue)</p>
  
  <p>Maybe this example will explain better what I'm trying to say:
  <a href="https://codesandbox.io/s/thirsty-hamilton-m7bmc" rel="nofollow noreferrer">https://codesandbox.io/s/thirsty-hamilton-m7bmc</a></p>
  
  <p>If you add a field in the example and hit submit, it will complain the field is required. However it certainly does have a value in there, but apparently not for the Form state.</p>
  
  <p>I hope someone else has encountered a similar issue</p>