Per the IRS Instructions for Form 1040NR U.S. Nonresident Alien Income Tax Return (click the link and view the entire publication for additional details regarding the items below), page 7:

Who Must File Form 1040NR
 
You must file Form 1040NR if any of the following conditions apply to you.

1. You were a nonresident alien engaged in a trade or business in the United States during 2018. You must file even if:
   1. You have no income from a trade or business conducted in the United States,
   2. You have no U.S. source income, or
   3. Your income is exempt from U.S. tax under a tax treaty or any section of the Internal Revenue Code.
   However, if you have no gross income for 2018, do not complete the schedules for Form 1040NR. Instead, attach a list of the kinds of exclusions you claim and the amount of each.
2. You were a nonresident alien not engaged in a trade or business in the United States during 2018 and:
   1. You received income from U.S. sources that is reportable on Schedule NEC, lines 1 through 12, and
   2. Not all of the U.S. tax that you owe was withheld from that income.
3. You owe any special taxes, including any of the following.
   1. Alternative minimum tax.
   2. Additional tax on a qualified plan, including an individual retirement arrangement (IRA), or other tax-favored account. (If you are filing a return only because you owe this tax, you can file Form 5329 by itself.)
   3. Household employment taxes. (If you are filing a return only because you owe these taxes, you can file Schedule H (Form 1040) by itself.)
   4. Social security and Medicare tax on tips you did not report to your employer or on wages you received from an employer who did not withhold these taxes.
   5. Recapture of first-time homebuyer credit. See the instructions for line 59b.
   6. Write-in taxes or recapture taxes, including uncollected social security and Medicare or RRTA tax on tips you reported to your employer or on group-term life insurance and additional taxes on health savings accounts. See the instructions for line 60.
4. You received HSA, Archer MSA, or Medicare Advantage MSA distributions.
5. You had net earnings from self-employment of at least $400 and you are a resident of a country with whom the United States has an international social security agreement. See the instructions for line 55.
6. Advance payments of the premium tax credit were made for you, your spouse, or a dependent who enrolled in coverage through the Marketplace. You or whoever enrolled you should have received Form(s) 1095-A showing the amount of the advance payments.
7. Advance payments of the health coverage tax credit were made for you, your spouse, or a dependent. You or whoever enrolled you should have received Form(s) 1099-H showing the amount of the advance payments.
8. You are the personal representative for a deceased person who would have had to file Form 1040NR. A personal representative can be an executor, administrator, or anyone who is in charge of the deceased person's property.
9. You represent an estate or trust that has to file Form 1040NR. Change the form to reflect the provisions of Subchapter J, Chapter 1, of the Internal Revenue Code. You may find it helpful to refer to Form 1041 and its instructions when completing the Form 1040NR

Exceptions. You do not need to file Form 1040NR if you meet (1), (2), or (3) below.

1. You were a nonresident alien student, teacher, or trainee who was temporarily present in the United States under an “F,” “J,” “M,” or “Q” visa, and you have no income that is CAUTION ! subject to tax under section 871 (that is, the income items listed on page 1 of Form 1040NR, lines 8 through 21, and on page 4, Schedule NEC, lines 1 through 12).
2. You were a student or business apprentice who was eligible for the benefits of Article 21(2) of the U.S.-India Income Tax Treaty, you are single or a qualifying widow(er), and your gross income for 2018 was less than or equal to $12,000 if single ($24,000 if a qualifying widow(er)). See chapter 5 of Pub. 519 for more details on these Treaty benefits. 
3. You were a partner in a U.S. partnership that was not engaged in a trade or business in the United States during 2018 and your Schedule K-1 (Form 1065) includes only income from U.S. sources reportable on Schedule NEC, lines 1 through 12.
4. Your gross income was less than $5.

Exception for certain children under age 19 or full-time students. If your child was under age 19 at the end of 2018 or was a full-time student under age 24 at the end of 2018, had income only from interest and dividends that are effectively connected with a U.S. trade or business, and that income totaled less than $10,500, you can elect to report your child's income on your return. To do so, use Form 8814. If you make this election, your child does not have to file a return. For details, including the conditions for children under age 24, see Form 8814.

A child born on January 1, 1995, is considered to be age 24 at the end of 2018. Do not use Form 8814 for such a child.