Gracefully handle null values in cells

Author: jameskleeh

src/main/groovy/com/jameskleeh/excel/internal/CreatesCells.groovy

@@ -187,6 +187,9 @@ abstract class CreatesCells {
 
         XSSFCell cell = nextCell()
         setStyle(value, cell, style)
+        if (value == null) {
+            return
+        }
         Closure callable = Excel.getRenderer(value.class)
         if (callable != null) {
             cell.setCellValue((String)callable.call(value))

src/test/groovy/com/jameskleeh/excel/RowSpec.groovy

@@ -1,6 +1,7 @@
 package com.jameskleeh.excel
 
 import org.apache.poi.ss.usermodel.Cell
+import org.apache.poi.ss.usermodel.CellType
 import org.apache.poi.xssf.usermodel.XSSFSheet
 import org.apache.poi.xssf.usermodel.XSSFWorkbook
 import spock.lang.Specification
@@ -136,4 +137,22 @@ class RowSpec extends Specification {
         cells.next().stringCellValue == 'foox'
         cells.next().numericCellValue == new Double(1)
     }
+
+    void "test cell with null value"() {
+        given:
+        XSSFWorkbook workbook = ExcelBuilder.build {
+            sheet {
+                row {
+                    cell(null)
+                }
+            }
+        }
+
+        when:
+        Cell cell = workbook.getSheetAt(0).getRow(0).getCell(0)
+
+        then:
+        noExceptionThrown()
+        cell.getCellTypeEnum() == CellType.BLANK
+    }
 }