In mathematics and logic, a Vacuous Truth or "vacuously true statement" is a statement that is only true because the antecedent cannot be satisfied.
Example from Wikipedia:
For example, the statement "all cell phones in the room are turned off" will be true even if there are no cell phones in the room. In this case, the statement "all cell phones in the room are turned on" would also be vacuously true, as would the conjunction of the two: "all cell phones in the room are turned on and turned off". For that reason, it is sometimes said that a statement is vacuously true only because it does not really say anything.
As a side note, using vacuously true statements with insufficient context may invite assumptions about the antecedent, or imply that . As noted in comments by @Gregory Currie, if I heard the statement "All cell phones are turned on", my first assumption is that there is at least one, and probably more than one cell phone in the room. This side effect is sometimes used on purpose, to mislead the audience "without technically lying". For example, a teenager may say to their mom, "No, I promise I didn't come home too late last night!", without mentioning that they actually didn't come home last night at all. In this way, they avoid the sin/crime of lying to their parents, but avoid revealing the incriminating truth.
This effect is similar to Lying by Omission, in that it's commonly thought of as a type of deception, but somehow not as bad as telling an outright lie. As noted by @dbmag9, these are ways of slightly violating one or two of the Maxims of the Cooperative Principle, just not the specific Maxim that requires not telling lies.
This phrase is, unfortunately, not that common among people who didn't study math or logic. So perhaps this Answer itself is vacuously true, in the sense that the phrase technically fits, but likely doesn't solve your need.