field_changed? should check also string columns for changes from nil to ''

An empty string is treated as a null value in Oracle. So why not add " || column.type == :string" ?

def field_changed?(attr, old, value)
  if column = column_for_attribute(attr)
    if (column.type == :integer || column.type == :string) && column.null && (old.nil? || old == 0)
      # For nullable integer columns, NULL gets stored in database for blank (i.e. '') values.
      # Hence we don't record it as a change if the value changes from nil to ''.
      # If an old value of 0 is set to '' we want this to get changed to nil as otherwise it'll
      # be typecast back to 0 (''.to_i => 0)
      value = nil if value.blank?
    else
      value = column.type_cast(value)
    end
  end

  old != value
end