code: package it.unibz.inf.ontop.evaluator;
  
  import com.google.common.collect.ImmutableSet;
  import it.unibz.inf.ontop.model.term.ImmutableExpression;
  import it.unibz.inf.ontop.model.term.Variable;
  
  public interface TermNullabilityEvaluator {
  
      boolean isFilteringNullValue(ImmutableExpression expression, Variable variable);
  
      /**
       * tightVariables: if one is null the others as well
       */
      boolean isFilteringNullValues(ImmutableExpression expression, ImmutableSet<Variable> tightVariables);
  }
  