code: package it.unibz.inf.ontop.model.term.functionsymbol.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.iq.node.VariableNullability;
  import it.unibz.inf.ontop.model.term.Constant;
  import it.unibz.inf.ontop.model.term.ImmutableTerm;
  import it.unibz.inf.ontop.model.term.TermFactory;
  import it.unibz.inf.ontop.model.type.RDFTermType;
  import it.unibz.inf.ontop.model.type.TermTypeInference;
  import it.unibz.inf.ontop.model.vocabulary.SPARQL;
  import it.unibz.inf.ontop.utils.ImmutableCollectors;
  
  import java.util.Optional;
  import java.util.stream.IntStream;
  
  public class CoalesceSPARQLFunctionSymbolImpl extends SPARQLFunctionSymbolImpl {
  
      protected CoalesceSPARQLFunctionSymbolImpl(int arity, RDFTermType rootRDFTermType) {
          super("SP_COALESCE" + arity, SPARQL.COALESCE,
                  IntStream.range(0, arity)
                          .mapToObj(i -> rootRDFTermType)
                          .collect(ImmutableCollectors.toList()));
      }
  
      @Override
      protected final ImmutableTerm buildTermAfterEvaluation(ImmutableList<ImmutableTerm> newTerms,
                                                             TermFactory termFactory, VariableNullability variableNullability) {
          if (newTerms.stream().allMatch(ImmutableTerm::isNull))
              return termFactory.getNullConstant();
  
          if (newTerms.stream()
                  .allMatch(t -> isRDFFunctionalTerm(t) || (t instanceof Constant))) {
              ImmutableList<ImmutableTerm> typeTerms = newTerms.stream()
                      .map(t -> extractRDFTermTypeTerm(t, termFactory))
                      .collect(ImmutableCollectors.toList());
  
              ImmutableList<ImmutableTerm> subLexicalTerms = newTerms.stream()
                      .map(t -> extractLexicalTerm(t, termFactory))
                      .collect(ImmutableCollectors.toList());
  
              ImmutableTerm typeTerm = termFactory.getDBCoalesce(typeTerms);
              ImmutableTerm lexicalTerm = termFactory.getDBCoalesce(subLexicalTerms);
  
              return termFactory.getRDFFunctionalTerm(lexicalTerm, typeTerm)
                      .simplify(variableNullability);
          }
          else
              return termFactory.getImmutableFunctionalTerm(this, newTerms);
      }
  
      @Override
      public boolean isAlwaysInjectiveInTheAbsenceOfNonInjectiveFunctionalTerms() {
          return false;
      }
  
      /**
       * No inference at the moment, because it is too complex
       */
      @Override
      public Optional<TermTypeInference> inferType(ImmutableList<? extends ImmutableTerm> terms) {
          return Optional.empty();
      }
  
      @Override
      public boolean canBePostProcessed(ImmutableList<? extends ImmutableTerm> arguments) {
          return false;
      }
  
      @Override
      protected boolean tolerateNulls() {
          return true;
      }
  }
  