multicolumn PRIMARY KEY introduces wrong 'not null' fields

Laurent Martelli (laurent(at)bearteam(dot)org) reports a bug with a severity of 3
The lower the number the more severe it is.

Short Description
multicolumn PRIMARY KEY introduces wrong 'not null' fields

Long Description
If you have a primary key on several columns, each of these columns is given the 'not null' modifier. I can't see why this is required. In the example below, the 'Type' column is made 'not null'.

Sample Code
CREATE TABLE test (
Type integer,
PictureID integer NOT NULL REFERENCES pictures(PictureID),
Value character varying(128) NOT NULL,
PRIMARY KEY (Type,PictureID,Value));

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