docs: public Concept getConcept(Variable var) {
          var = equivalentVars.componentOf(var);
          assert var != null;
  
          @Nullable Concept concept = concepts.get(var);
  
          if (concept == null) {
              @Nullable ConceptBuilder builder = conceptBuilders.remove(var);
  
              if (builder != null) {
                  concept = buildConcept(var, builder);
              }
          }
  
          if (concept != null) {
              return concept;
          }
  
          LOG.debug("Could not build concept for {}\nconcepts = {}\nconceptBuilders = {}", var, concepts, conceptBuilders);
  
          throw GraqlQueryException.insertUndefinedVariable(printableRepresentation(var));
      }