Discover parameter: missings and missing_value

[abenassi]

• Presence of missings can be determined by following a data series values together with the time index values. Whenever a data value is a string that cannot be converted to a float but there is a valid time index value on the same row, we are in the presence of a missing value.
• If the time index values are not contiguous at some point (non consecutive but future time value comes next after another valid time value) we have "Implicit" missing values (because there are holes in the time representation).