output: #fixed code
                                @Test
    public void handleAllFieldsMappingSettingAndTheMappingsProvided() {
      List<DbTableColumn> columns = Lists.newArrayList(
          new DbTableColumn("col1", true, false, 1),
          new DbTableColumn("col2", false, false, 1),
          new DbTableColumn("col3", false, false, 1));
      DbTable table = new DbTable("tableA", columns);
  
      Map<String, FieldAlias> aliasMap = new HashMap<>();
      aliasMap.put("f1", new FieldAlias("col3"));
      FieldsMappings mappings = new FieldsMappings("tableA", "topic1", true, aliasMap);
  
      FieldsMappings newMappings = PreparedStatementBuilderHelper.validateAndMerge(mappings, table, InsertModeEnum.INSERT);
      assertEquals(newMappings.getTableName(), mappings.getTableName());
      assertEquals(newMappings.getIncomingTopic(), mappings.getIncomingTopic());
      assertEquals(newMappings.areAllFieldsIncluded(), false);
  
      Map<String, FieldAlias> newAliasMap = newMappings.getMappings();
      assertEquals(4, newAliasMap.size()); //+ the specific mapping
      assertTrue(newAliasMap.containsKey("col1"));
      assertEquals(newAliasMap.get("col1").getName(), "col1");
      assertEquals(newAliasMap.get("col1").isPrimaryKey(), true);
  
      assertTrue(newAliasMap.containsKey("col2"));
      assertEquals(newAliasMap.get("col2").getName(), "col2");
      assertEquals(newAliasMap.get("col2").isPrimaryKey(), false);
  
      assertTrue(newAliasMap.containsKey("col3"));
      assertEquals(newAliasMap.get("col3").getName(), "col3");
      assertEquals(newAliasMap.get("col3").isPrimaryKey(), false);
  
      assertTrue(newAliasMap.containsKey("f1"));
      assertEquals(newAliasMap.get("f1").getName(), "col3");
      assertEquals(newAliasMap.get("f1").isPrimaryKey(), false);
    }
input: #vulnerable code 
                                @Test
    public void handleAllFieldsMappingSettingAndTheMappingsProvided() {
      List<DbTableColumn> columns = Lists.newArrayList(
          new DbTableColumn("col1", true, false, 1),
          new DbTableColumn("col2", false, false, 1),
          new DbTableColumn("col3", false, false, 1));
      DbTable table = new DbTable("tableA", columns);
  
      Map<String, FieldAlias> aliasMap = new HashMap<>();
      aliasMap.put("f1", new FieldAlias("col3"));
      FieldsMappings mappings = new FieldsMappings("tableA", "topic1", true, aliasMap);
  
      FieldsMappings newMappings = PreparedStatementBuilderHelper.validateAndMerge(mappings, table);
      assertEquals(newMappings.getTableName(), mappings.getTableName());
      assertEquals(newMappings.getIncomingTopic(), mappings.getIncomingTopic());
      assertEquals(newMappings.areAllFieldsIncluded(), false);
  
      Map<String, FieldAlias> newAliasMap = newMappings.getMappings();
      assertEquals(4, newAliasMap.size()); //+ the specific mapping
      assertTrue(newAliasMap.containsKey("col1"));
      assertEquals(newAliasMap.get("col1").getName(), "col1");
      assertEquals(newAliasMap.get("col1").isPrimaryKey(), true);
  
      assertTrue(newAliasMap.containsKey("col2"));
      assertEquals(newAliasMap.get("col2").getName(), "col2");
      assertEquals(newAliasMap.get("col2").isPrimaryKey(), false);
  
      assertTrue(newAliasMap.containsKey("col3"));
      assertEquals(newAliasMap.get("col3").getName(), "col3");
      assertEquals(newAliasMap.get("col3").isPrimaryKey(), false);
  
      assertTrue(newAliasMap.containsKey("f1"));
      assertEquals(newAliasMap.get("f1").getName(), "col3");
      assertEquals(newAliasMap.get("f1").isPrimaryKey(), false);
    } 
                              #location 21 
                              #vulnerability type NULL_DEREFERENCE