The Input Features you specified has eight or less valid features. To test for spatial autocorrelation in model residuals, a default spatial weights matrix based on eight nearest neighbors is used. When there are eight or fewer features, this default is set to the number of features minus two. Note that features with NULL values for any of the fields specified are not valid and will be skipped.
In general, you should not use this tool with less than 30 features. If your feature class has eight or more features and you see this message, it is likely because of NULL values in the fields you specified. Exclude fields with NULL values or correct the NULL values by replacing them with actual numbers.