NCI-Agency/anet#1726: Fix warning about duration field in report form
NCI-Agency/anet#1726: Fix warning about duration field in report form

This fixes the following warning: Warning: `value` prop on `input`
should not be null. Consider using an empty string to clear the
component or `undefined` for uncontrolled components.

NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet,NCI-Agency/anet