What's a nightwalker?

Taken directly from The General Laws of Massachusetts: Chapter 272, Section 62

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CHAPTER 272.CRIMES AGAINST CHASTITY, MORALITY, DECENCY AND GOOD ORDER

Chapter 272: Section 62 Third conviction of being a common nightwalker

  Section 62. If a complaint charges a person with being a common nightwalker, and it is proved at the trial that such person has been twice before convicted of the same offence, such person may be sentenced to the house of correction for not more than two and one half years or if a male, to the Massachusetts reformatory, or if a female, to the reformatory for women.