The YAML format contains a value null to represent missing data. The YAML:-null symbol in Maple is used to represent YAML null symbols after import into Maple.

The commands YAML:-ParseString and YAML:-ParseFile may produce output which uses YAML:-null.

The YAML:-ToString command recognizes YAML:-null and translates it to null in YAML.

YAML:-ParseString("[2,3,null,5,null,7]");

$\left[2\,3\,\mathrm{YAML}:-\mathrm{null}\,5\,\mathrm{YAML}:-\mathrm{null}\,7\right]$

Beowulf := table([ "title" = "Beowulf", "language" = "Anglo-Saxon", "author" = YAML:-null ]);

$\mathrm{Beowulf}≔table\left(\left[''language''=''Anglo-Saxon''\,''title''=''Beowulf''\,''author''=\mathrm{YAML}:-\mathrm{null}\right]\right)$

YAML:-ToString( Beowulf );

$''---\; author:\; null\; language:\; "Anglo-Saxon"\; title:\; Beowulf''$

The YAML[null] command was introduced in Maple 2017.

For more information on Maple 2017 changes, see Updates in Maple 2017.