A person in possession of real property, claiming an estate of freehold therein or an unexpired term of not less than 10 years, or a person who has conveyed such property or any interest therein with covenants of title or warranty, upon which he may be liable, may, if he or those under whom he claims or those claiming under him have been in uninterrupted possession of such property for 4 years or more, bring an action in the Superior Court, or in the District Court in the county or district respectively in which said real property lies, setting forth his estate, stating the source of his title, describing the premises, and averring that an apprehension exists that persons named in the complaint, or persons unknown claiming as heirs, devisees or assigns, or in any other way, by, through or under a person or persons named in the complaint, claim or may claim some right, title or interest in the premises adverse to his said estate; and that such apprehension creates a cloud upon the title and depreciates the market value of the property; and praying that such persons be summoned to show cause why they should not bring an action to try their title to the described premises. If any such supposed claimants are unknown, the plaintiff or his attorney shall so allege under oath, but the truth of the allegation shall not after decree has been filed be denied for the purpose of defeating the title established thereby. A person in the enjoyment of an easement is in possession of real property within the meaning and for the purposes of this section. [PL 1971, c. 117, §2 (AMD).]