<xsd:documentation>An empty string is the default representation of a null value for a
curve (i.e., when the null value representation is not explicitly defined).
If a null value is defined in the logCurveInfo, it overrides any null value specified at the
logHeader level. An empty string is always a valid null value representation in the comma delimited list.
An empty string is not a valid null value representation within a space delimited array.
Specifying a null value also makes it easier to transform data back to a
legacy format without having to scan the data to insure that the null pattern
does not exist in the data. </xsd:documentation>