output: #fixed code
                                  private List<RuntimeException> validateModelWithDependencies(
              Executable executable,
              Map<String, Executable> dependencies,
              Set<Executable> verifiedExecutables,
              List<RuntimeException> errors) {
          //validate that all required & non private parameters with no default value of a reference are provided
          if(!SlangTextualKeys.FLOW_TYPE.equals(executable.getType()) || verifiedExecutables.contains(executable)){
              return errors;
          }
          verifiedExecutables.add(executable);
  
          Flow flow = (Flow) executable;
          Collection<Step> steps = flow.getWorkflow().getSteps();
          Set<Executable> flowReferences = new HashSet<>();
  
          for (Step step : steps) {
              String refId = step.getRefId();
              Executable reference = dependencies.get(refId);
  
              try {
                  validateMandatoryInputsAreWired(flow, step, reference);
                  validateStepInputNamesDifferentFromDependencyOutputNames(flow, step, reference);
                  validateDependenciesResultsHaveMatchingNavigations(executable, refId, step, reference);
              } catch (RuntimeException e) {
                  errors.add(e);
              }
  
              flowReferences.add(reference);
          }
  
          for (Executable reference : flowReferences) {
              validateModelWithDependencies(reference, dependencies, verifiedExecutables, errors);
          }
          return errors;
      }
input: #vulnerable code 
                                  private List<RuntimeException> validateModelWithDependencies(
              Executable executable,
              Map<String, Executable> dependencies,
              Set<Executable> verifiedExecutables,
              List<RuntimeException> errors) {
          //validate that all required & non private parameters with no default value of a reference are provided
          if(!SlangTextualKeys.FLOW_TYPE.equals(executable.getType()) || verifiedExecutables.contains(executable)){
              return errors;
          }
          verifiedExecutables.add(executable);
  
          Flow flow = (Flow) executable;
          Collection<Step> steps = flow.getWorkflow().getSteps();
          Set<Executable> flowReferences = new HashSet<>();
  
          for (Step step : steps) {
              String refId = step.getRefId();
              Executable reference = dependencies.get(refId);
              List<String> mandatoryInputNames = getMandatoryInputNames(reference);
              List<String> stepInputNames = getStepInputNames(step);
              List<String> inputsNotWired = getInputsNotWired(mandatoryInputNames, stepInputNames);
  
              try {
                  validateInputNamesEmpty(inputsNotWired, flow, step, reference);
                  validateStepInputNamesDifferentFromDependencyOutputNames(flow, step, reference);
                  validateDependenciesResultsHaveMatchingNavigations(executable, refId, step, reference);
              } catch (RuntimeException e) {
                  errors.add(e);
              }
  
              flowReferences.add(reference);
          }
  
          for (Executable reference : flowReferences) {
              validateModelWithDependencies(reference, dependencies, verifiedExecutables, errors);
          }
          return errors;
      } 
                              #location 19 
                              #vulnerability type NULL_DEREFERENCE