2.2.13.3.1.5 NULL Predicate

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The NULL predicate MUST be true if the item doesn’t have a value for the specified property. Its basic syntax is as follows:

 …property IS NULL…

It has an alternate syntax that reverses its meaning. The alternate syntax is as follows:

 …property IS NOT NULL…

If this predicate is used with the properties Path, Rank, ContentClass or SiteName, the query MUST return with the ERROR_SERVER error code.

If this predicate is used with the WorkId property, the query MUST return with the ERROR_BAD_QUERY error code.

If this predicate is used with the properties HitHighlightedSummary or HitHighlightedProperties, it MUST be true regardless of the value of the specified property.

If this predicate is used with the PictureThumbnailURL property, it MUST be false regardless of the value of the specified property.

 null-predicate           =   identifier 1*ws "IS" 1*ws ["NOT" 1*ws] "NULL"