output: #fixed code
                                @Test
    public void shouldReturnThePrimaryKeysAtTheEndWhenMultipleFieldsFormThePrimaryKey() {
      Schema schema = SchemaBuilder.struct().name("com.example.Person")
              .field("firstName", Schema.STRING_SCHEMA)
              .field("lastName", Schema.STRING_SCHEMA)
              .field("age", Schema.INT32_SCHEMA)
              .field("bool", Schema.BOOLEAN_SCHEMA)
              .field("short", Schema.INT16_SCHEMA)
              .field("byte", Schema.INT8_SCHEMA)
              .field("long", Schema.INT64_SCHEMA)
              .field("float", Schema.FLOAT32_SCHEMA)
              .field("double", Schema.FLOAT64_SCHEMA)
              .field("bytes", Schema.BYTES_SCHEMA)
              .field("threshold", Schema.OPTIONAL_FLOAT64_SCHEMA).build();
  
      short s = 1234;
      byte b = -32;
      long l = 12425436;
      float f = (float) 2356.3;
      double d = -2436546.56457;
      byte[] bs = new byte[]{-32, 124};
  
      Struct struct = new Struct(schema)
              .put("firstName", "Alex")
              .put("lastName", "Smith")
              .put("bool", true)
              .put("short", s)
              .put("byte", b)
              .put("long", l)
              .put("float", f)
              .put("double", d)
              .put("bytes", bs)
              .put("age", 30);
  
      Map<String, FieldAlias> mappings = new HashMap<>();
      mappings.put("firstName", new FieldAlias("fName", true));
      mappings.put("lastName", new FieldAlias("lName", true));
  
      FieldsMappings tm = new FieldsMappings("table", "topic", true, mappings);
      StructFieldsDataExtractor dataExtractor = new StructFieldsDataExtractor(tm);
      List<PreparedStatementBinder> binders = dataExtractor.get(struct,
              new SinkRecord("", 1, null, null, schema, struct, 0));
  
      HashMap<String, PreparedStatementBinder> map = new HashMap<>();
      List<PreparedStatementBinder> pkBinders = new LinkedList<>();
      for (PreparedStatementBinder p : binders) {
        if (p.isPrimaryKey()) {
          pkBinders.add(p);
        }
        map.put(p.getFieldName(), p);
      }
  
      assertTrue(!binders.isEmpty());
      assertEquals(binders.size(), 10);
  
      assertEquals(pkBinders.size(), 2);
  
      assertTrue(Objects.equals(pkBinders.get(0).getFieldName(), "fName") ||
              Objects.equals(pkBinders.get(1).getFieldName(), "fName")
      );
  
      assertTrue(Objects.equals(pkBinders.get(0).getFieldName(), "lName") ||
              Objects.equals(pkBinders.get(1).getFieldName(), "lName")
      );
  
      assertTrue(map.containsKey("fName"));
      assertTrue(map.get("fName").getClass() == StringPreparedStatementBinder.class);
  
      assertTrue(map.containsKey("lName"));
      assertTrue(map.get("lName").getClass() == StringPreparedStatementBinder.class);
  
      assertTrue(map.containsKey("age"));
      assertTrue(map.get("age").getClass() == IntPreparedStatementBinder.class);
  
      assertTrue(map.get("long").getClass() == LongPreparedStatementBinder.class);
      assertEquals(((LongPreparedStatementBinder) map.get("long")).getValue(), l);
  
      assertTrue(map.get("short").getClass() == ShortPreparedStatementBinder.class);
      assertEquals(((ShortPreparedStatementBinder) map.get("short")).getValue(), s);
  
      assertTrue(map.get("byte").getClass() == BytePreparedStatementBinder.class);
      assertEquals(((BytePreparedStatementBinder) map.get("byte")).getValue(), b);
  
      assertTrue(map.get("float").getClass() == FloatPreparedStatementBinder.class);
      assertEquals(Float.compare(((FloatPreparedStatementBinder) map.get("float")).getValue(), f), 0);
  
      assertTrue(map.get("double").getClass() == DoublePreparedStatementBinder.class);
      assertEquals(Double.compare(((DoublePreparedStatementBinder) map.get("double")).getValue(), d), 0);
  
      assertTrue(map.get("bytes").getClass() == BytesPreparedStatementBinder.class);
      assertTrue(Arrays.equals(bs, ((BytesPreparedStatementBinder) map.get("bytes")).getValue()));
    }
input: #vulnerable code 
                                @Test
    public void shouldReturnThePrimaryKeysAtTheEndWhenMultipleFieldsFormThePrimaryKey() {
      Schema schema = SchemaBuilder.struct().name("com.example.Person")
              .field("firstName", Schema.STRING_SCHEMA)
              .field("lastName", Schema.STRING_SCHEMA)
              .field("age", Schema.INT32_SCHEMA)
              .field("bool", Schema.BOOLEAN_SCHEMA)
              .field("short", Schema.INT16_SCHEMA)
              .field("byte", Schema.INT8_SCHEMA)
              .field("long", Schema.INT64_SCHEMA)
              .field("float", Schema.FLOAT32_SCHEMA)
              .field("double", Schema.FLOAT64_SCHEMA)
              .field("bytes", Schema.BYTES_SCHEMA)
              .field("threshold", Schema.OPTIONAL_FLOAT64_SCHEMA).build();
  
      short s = 1234;
      byte b = -32;
      long l = 12425436;
      float f = (float) 2356.3;
      double d = -2436546.56457;
      byte[] bs = new byte[]{-32, 124};
  
      Struct struct = new Struct(schema)
              .put("firstName", "Alex")
              .put("lastName", "Smith")
              .put("bool", true)
              .put("short", s)
              .put("byte", b)
              .put("long", l)
              .put("float", f)
              .put("double", d)
              .put("bytes", bs)
              .put("age", 30);
  
      Map<String, FieldAlias> mappings = new HashMap<>();
      mappings.put("firstName", new FieldAlias("fName", true));
      mappings.put("lastName", new FieldAlias("lName", true));
  
      FieldsMappings tm = new FieldsMappings("table", "topic", true, mappings);
      StructFieldsDataExtractor dataExtractor = new StructFieldsDataExtractor(tm);
      StructFieldsDataExtractor.PreparedStatementBinders binders = dataExtractor.get(struct,
              new SinkRecord("", 1, null, null, schema, struct, 0));
  
      HashMap<String, PreparedStatementBinder> map = new HashMap<>();
      for (PreparedStatementBinder p : Iterables.concat(binders.getNonKeyColumns(), binders.getKeyColumns()))
        map.put(p.getFieldName(), p);
  
      assertTrue(!binders.isEmpty());
      assertEquals(binders.getNonKeyColumns().size() + binders.getKeyColumns().size(), 10);
  
      List<PreparedStatementBinder> pkBinders = binders.getKeyColumns();
      assertEquals(pkBinders.size(), 2);
  
      assertTrue(Objects.equals(pkBinders.get(0).getFieldName(), "fName") ||
              Objects.equals(pkBinders.get(1).getFieldName(), "fName")
      );
  
      assertTrue(Objects.equals(pkBinders.get(0).getFieldName(), "lName") ||
              Objects.equals(pkBinders.get(1).getFieldName(), "lName")
      );
  
      assertTrue(map.containsKey("fName"));
      assertTrue(map.get("fName").getClass() == StringPreparedStatementBinder.class);
  
      assertTrue(map.containsKey("lName"));
      assertTrue(map.get("lName").getClass() == StringPreparedStatementBinder.class);
  
      assertTrue(map.containsKey("age"));
      assertTrue(map.get("age").getClass() == IntPreparedStatementBinder.class);
  
      assertTrue(map.get("long").getClass() == LongPreparedStatementBinder.class);
      assertEquals(((LongPreparedStatementBinder) map.get("long")).getValue(), l);
  
      assertTrue(map.get("short").getClass() == ShortPreparedStatementBinder.class);
      assertEquals(((ShortPreparedStatementBinder) map.get("short")).getValue(), s);
  
      assertTrue(map.get("byte").getClass() == BytePreparedStatementBinder.class);
      assertEquals(((BytePreparedStatementBinder) map.get("byte")).getValue(), b);
  
      assertTrue(map.get("float").getClass() == FloatPreparedStatementBinder.class);
      assertEquals(Float.compare(((FloatPreparedStatementBinder) map.get("float")).getValue(), f), 0);
  
      assertTrue(map.get("double").getClass() == DoublePreparedStatementBinder.class);
      assertEquals(Double.compare(((DoublePreparedStatementBinder) map.get("double")).getValue(), d), 0);
  
      assertTrue(map.get("bytes").getClass() == BytesPreparedStatementBinder.class);
      assertTrue(Arrays.equals(bs, ((BytesPreparedStatementBinder) map.get("bytes")).getValue()));
    } 
                              #location 49 
                              #vulnerability type NULL_DEREFERENCE