fix #234 when return null reference

src/main/java/com/poiji/bind/mapping/PoijiHandler.java

@@ -199,6 +199,10 @@ public void endRow(int rowNum) {
 
     @Override
     public void cell(String cellReference, String formattedValue, XSSFComment comment) {
+        if (cellReference == null) {
+            // TODO hidden log required; a cell reference could return null
+            return;
+        }
         final CellAddress cellAddress = new CellAddress(cellReference);
         int row = cellAddress.getRow();
         int headerStart = options.getHeaderStart();

src/main/java/com/poiji/bind/mapping/XSSFSheetXMLPoijiHandler.java

@@ -57,7 +57,9 @@ public void startElement(String uri, String localName, String qName, Attributes
                         int styleIndex = Integer.parseInt(cellStyleStr);
 
                         if (poijiOptions.isDisableXLSXNumberCellFormat()) {
-                            attributes2.removeAttribute(styleIndex);
+                            if (attributes2.getLength() > styleIndex) {
+                                attributes2.removeAttribute(styleIndex);
+                            }
                         }
                     }
                 }

src/test/java/com/poiji/deserialize/NullReferenceTest.java

@@ -0,0 +1,27 @@
+package com.poiji.deserialize;
+
+import com.poiji.bind.Poiji;
+import com.poiji.deserialize.model.AutoImport;
+import com.poiji.option.PoijiOptions;
+import org.junit.Test;
+
+import java.io.File;
+import java.util.List;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.junit.Assert.assertNotNull;
+
+public class NullReferenceTest {
+
+    @Test
+    public void shouldReturnEmptyWhenCellReferenceNull() {
+        PoijiOptions options = PoijiOptions.PoijiOptionsBuilder.settings().disableXLSXNumberCellFormat().build();
+
+        List<AutoImport> result = Poiji.fromExcel(new File("src/test/resources/autos2.xlsx"), AutoImport.class, options);
+
+        assertNotNull(result);
+        assertThat(result.size(), is(20));
+
+    }
+}

src/test/java/com/poiji/deserialize/model/AutoImport.java

@@ -0,0 +1,58 @@
+package com.poiji.deserialize.model;
+
+import com.poiji.annotation.ExcelCell;
+import com.poiji.annotation.ExcelCellName;
+
+import java.time.LocalDate;
+
+public class AutoImport {
+
+    @ExcelCellName(value = "fabricacion", mandatory = false)
+    private LocalDate fecha;
+
+    @ExcelCell(0)
+    private String clase;
+
+    @ExcelCell(1)
+    private String tipo;
+
+    @ExcelCell(2)
+    private String subtipo;
+
+    @ExcelCell(3)
+    private String marca;
+
+    @ExcelCell(4)
+    private String modelo;
+
+    @ExcelCell(5)
+    private String submodelo;
+
+    @ExcelCell(6)
+    private String dsc;
+
+    @ExcelCell(7)
+    private String pmercado;
+
+    @ExcelCell(8)
+    private Double ptoma;
+
+    @ExcelCell(9)
+    private String anio;
+
+    @ExcelCell(10)
+    private String cil;
+
+    @ExcelCell(11)
+    private String com;
+
+    @ExcelCell(12)
+    private String tp;
+
+    @ExcelCell(13)
+    private Integer pasajeros;
+
+    @ExcelCell(14)
+    private Integer puertas;
+
+}