Merge pull request #1787 from jaaaar/master

fix.处理空值不受指定converter处理的问题

src/main/java/com/alibaba/excel/write/executor/AbstractExcelWriteExecutor.java

@@ -33,9 +33,6 @@ public abstract class AbstractExcelWriteExecutor implements ExcelWriteExecutor {
     protected CellData<?> converterAndSet(WriteHolder currentWriteHolder, Class<?> clazz, CellDataTypeEnum targetType,
         Cell cell, Object value,
         ExcelContentProperty excelContentProperty, Head head, Integer relativeRowIndex) {
-        if (value == null) {
-            return new CellData<>(CellDataTypeEnum.EMPTY);
-        }
         if (value instanceof String && currentWriteHolder.globalConfiguration().getAutoTrim()) {
             value = ((String)value).trim();
         }
@@ -75,9 +72,6 @@ public abstract class AbstractExcelWriteExecutor implements ExcelWriteExecutor {
     protected CellData<?> convert(WriteHolder currentWriteHolder, Class<?> clazz, CellDataTypeEnum targetType,
         Cell cell,
         Object value, ExcelContentProperty excelContentProperty) {
-        if (value == null) {
-            return new CellData<>(CellDataTypeEnum.EMPTY);
-        }
         // This means that the user has defined the data.
         if (value instanceof CellData) {
             CellData<?> cellDataValue = (CellData<?>)value;