code: package it.unibz.inf.ontop.model.term.functionsymbol.db.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.iq.node.VariableNullability;
  import it.unibz.inf.ontop.model.term.*;
  import it.unibz.inf.ontop.model.type.DBTermType;
  
  public class NullToleratingDBConcatFunctionSymbol extends AbstractDBConcatFunctionSymbol {
  
      protected NullToleratingDBConcatFunctionSymbol(String nameInDialect, int arity, DBTermType dbStringType,
                                                     DBTermType rootDBTermType, boolean isOperator) {
          super(nameInDialect, arity, dbStringType, rootDBTermType,
                  isOperator
                          ? Serializers.getOperatorSerializer(nameInDialect)
                          : Serializers.getRegularSerializer(nameInDialect));
      }
  
      @Override
      public boolean isAlwaysInjectiveInTheAbsenceOfNonInjectiveFunctionalTerms() {
          return false;
      }
  
      @Override
      public boolean canBePostProcessed(ImmutableList<? extends ImmutableTerm> arguments) {
          return true;
      }
  
      @Override
      protected boolean tolerateNulls() {
          return true;
      }
  
      /**
       * Never returns NULL
       */
      public IncrementalEvaluation evaluateIsNotNull(ImmutableList<? extends ImmutableTerm> terms, TermFactory termFactory,
                                                     VariableNullability variableNullability) {
          return IncrementalEvaluation.declareIsTrue();
      }
  
      @Override
      protected String extractString(Constant constant) {
          return constant.isNull()
                  ? ""
                  : constant.getValue();
      }
  }
  