Question: What was the nationality of the stage partner of the director of "Tim's Vermeer"?

Context paragraphs:
Ning Cai (magician): Ning Cai (Chinese: 蔡嬣; born 1982), better known as Mind Magic Mistress (and formerly known as Magic Babe Ning), is a Singaporean magician, illusionist, escape artist and entrepreneur.  She has been recognised by Channel News Asia as South East Asia's first professional female magician.  Along with her former stage partner J C Sum, Cai has been credited for popularising magic in Singapore.  She is best known for her good looks and for bringing glamour to magic in Asia, and was named "the sexiest woman in magic" by UK magic magazine "MagicSeen"; she was subsequently described this way by multiple publications in Singapore.

Oliver Knight: Oliver Knight (born 1969) is a British singer-songwriter and sound engineer.  He is son to folk singer/songwriter Lal Waterson and George Knight.  He is brother and stage partner to folk musician Marry Waterson.

Antonio Giuglini: Antonio Giuglini (16 or 17 January 1825 – 12 October 1865) was an Italian operatic tenor.  During the last eight years of his life, before he developed signs of mental instability, he earned renown as one of the leading stars of the operatic scene in London.  He created several major roles for British audiences, appearing in the first London performances of Gounod's "Faust" and Verdi's "Un ballo in maschera".  In London, he was the usual stage partner of the great dramatic soprano Thérèse Tietjens.

Coptic Soldier: Luke George Girgis (born 20 August 1987), better known by his stage name, Coptic Soldier, is an Australian hip-hop artist, music manager and record label executive.  He often performed with stage partner, Phatchance (aka Chance Waters) and later became his manager.  Girgis co-founded a record label, I Forgot Sorry!  in 2010 and then a management company, Be Like Children, in 2013.

Opinit: Opinit is an emotion-based platform created by Paolo Fidanza and Qualid Ladraa.  Paolo and Qualid, who goes by the name of Q, incubated the idea of creating a new way to categorize and consume content based on emotion tags in early 2014.  In June 2014, Paolo and Q founded Opinit, Inc. in Los Angeles, California, with Paolo as CEO and Q as CMO, and started development of the platform.  In October 2014, Andrew Kurinnyi joined as CTO to lead technology development, and Slimane Bennis joined as an early stage partner.  In May 2015, a first version of Opinit for the iOS platform was released to a small group of beta testers.  After successful testing, at the end of June 2015, Opinit was approved by Apple and released in the Apple Store for download on iPhone, iPad, and iPod Touch.

Tim's Vermeer: Tim's Vermeer is a documentary film, directed by Teller, produced by his stage partner Penn Jillette and Farley Ziegler, about inventor Tim Jenison's efforts to duplicate the painting techniques of Johannes Vermeer, in order to test his theory that Vermeer painted with the help of optical devices.

Engel Lund: EngelLund (14 July 1900 – 15 June 1996) was a Danish-Icelandic soprano and a collector and distinguished interpreter of traditional music.  Her most notable work is the "Book of Folk Songs", a collection of 49 pieces with piano accompaniments by her stage partner, Austrian composer and pianist Ferdinand Rauter.  It was first published in 1936 by Oxford University Press.

Lidiya Sukharevskaya: Lidiya Sukharevskaya (30 August 1909 – 10 October 1991) was a Soviet stage actress and playwright renowned for her work with Nikolay Akimov and Andrey Goncharov.  Her frequent stage partner was Boris Tenin, her husband.  She also appeared in 14 films between 1939 and 1981.  Sukharevskaya was named a People's Artist of the USSR in 1990.

Bessie Thomashefsky: Bessie Thomashefsky (1873 – July 6, 1962) was a Russian-born Jewish American singer, actress and comedian, a star in Yiddish theater beginning in the 1890s.  She was the wife and stage partner of Boris Thomashefsky, the most popular Yiddish leading man of his era.  Probably her most famous role was the title role of Oscar Wilde's "Salomé" at the People’s Theater in 1908.

Penn Jillette: Penn Fraser Jillette (born March 5, 1955) is an American magician/illusionist, juggler, comedian, musician, inventor, actor, and best-selling author known for his work with fellow magician Teller as half of the team Penn & Teller.  He is also known for his advocacy of atheism, scientific skepticism, libertarianism, and free-market capitalism.

Supporting paragraphs: Tim's Vermeer Penn Jillette
Answer: American