Third edition of Artificial Intelligence: foundations of computational agents, Cambridge University Press, 2023 is now available (including the full text).
11.2.3 Missing Data
Data can be incomplete in ways other than having an unobserved variable. A data set can simply be missing the values of some variables for some of the tuples. When some of the values of the variables are missing, one must be very careful in using the data set because the missing data may be correlated with the phenomenon of interest.
If the data is missing at random, the missing data can be ignored. However, "missing at random" is a strong assumption. In general, an agent should construct a model of why the data is missing or, preferably, it should go out into the world and find out why the data is missing.