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Null.Type is a type facet in the Power Query M language. It represents the default type claim for the ‘type null’. It is used primarily for handling missing or undefined data within Power Query M. The base type of ‘type null’ in Power Query signifies a null or non-existent value.


Generally, you will face a facet when transforming column types. You can transform a column into the specified type by using Table.TransformColumnTypes:

Table.TransformColumnTypes( Source, {{ "myColumn", Null.Type }} )

Or when adding a column using Table.AddColumn:

Table.AddColumn( Source, "myColumn", null, Null.Type" )

To inspect the kind of value you are dealing with, you can make use of the Table.Schema function. Applying it to a table returns a table with information about your columns. The Table.SingleRow function then transforms the result into a record, for easier reading.

  a =  null,
   // Ascribes the default type claim facet for 'type null'
  b = Value.ReplaceType( a, Null.Type ),
  // Returns a table containing a value with the ascribed "Null.Type" 
  c = #table(type table [Col1 = Value.Type( b ) ], { b } ), 
  // Shows the Table information, including typeName and value kind
  d = Table.Schema( c ),
  // For easier viewing, return table as record
  e = Table.SingleRow( d )

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