Blank drug order frequencies and dosing units should be converted to null during upgrade

Ddrug order frequencies and dosing units values that are empty strings or white space characters should be converted to null during upgrade.

Dev Notes:

• Update MigrateDrugOrderUnitsToCodedDoseUnitsChangeset and MigrateDrugOrderFrequencyToCodedOrderFrequencyChangeset to set units and frequencies to null for empty strings and white space characters