Sovereign immunity — Diplomatic immunity — Foreign State and its Trade Representation — Restrictive theory of immunity — Contract with U.S.S.R. and its Trade Representation — Action to recover outstanding commission on contract and damages for alleged breach of contract — Whether action defeated by claim of sovereign immunity — Pakistan Civil Procedure Code, Section 86 — Whether applicable to actions against foreign States — International law in general — Relation to municipal law — Effect of trade agreement between Pakistan and the U.S.S.R. — Effect of Vienna Convention on Diplomatic Relations, 1961, and diplomatic certificate issued by Government of Pakistan — Whether the agreement, the Convention or the diplomatic certificate confers immunity from jurisdiction in a commercial and trade transaction — The law of Pakistan