Read empty string as null (#555)

README.md

@@ -1250,7 +1250,16 @@ var config = new MiniExcelLibs.Csv.CsvConfiguration()
 MiniExcel.SaveAs(path, value,excelType:ExcelType.CSV, configuration: config);
 ```
 
+#### Read empty string as null
 
+By default, empty values are mapped to string.Empty. You can modify this behavior
+
+```csharp
+var config = new MiniExcelLibs.Csv.CsvConfiguration()
+{
+   ReadEmptyStringAsNull = true
+};
+```
 
 
 ### DataReader

src/MiniExcel/Csv/CsvConfiguration.cs

@@ -10,6 +10,7 @@ public class CsvConfiguration : Configuration
 
         public char Seperator { get; set; } = ',';
         public string NewLine { get; set; } = "\r\n";
+        public bool ReadEmptyStringAsNull { get; set; } = false;
         public bool AlwaysQuote { get; set; } = false;
         public Func<string, string[]> SplitFn { get; set; }
         public Func<Stream, StreamReader> StreamReaderFunc { get; set; } = (stream) => new StreamReader(stream, _defaultEncoding);

src/MiniExcel/Csv/CsvReader.cs

@@ -59,8 +59,17 @@ public IEnumerable<IDictionary<string, object>> Query(bool useHeaderRow, string
                     //body
                     {
                         var cell = CustomPropertyHelper.GetEmptyExpandoObject(read.Length - 1, 0);
-                        for (int i = 0; i <= read.Length - 1; i++)
-                            cell[ColumnHelper.GetAlphabetColumnName(i)] = read[i];
+                        if (_config.ReadEmptyStringAsNull)
+                        {
+                            for (int i = 0; i <= read.Length - 1; i++)
+                                cell[ColumnHelper.GetAlphabetColumnName(i)] = read[i]?.Length == 0 ? null : read[i];
+                        }
+                        else
+                        {
+                            for (int i = 0; i <= read.Length - 1; i++)
+                                cell[ColumnHelper.GetAlphabetColumnName(i)] = read[i];
+                        }
+
                         yield return cell;
                     }
                 }

tests/MiniExcelTests/MiniExcelCsvAsycTests.cs

@@ -269,5 +269,55 @@ await MiniExcel.SaveAsAsync(path, new[] {
 
             File.Delete(path);
         }
+
+        [Fact()]
+        public async Task CsvReadEmptyStringAsNullTest()
+        {
+            var path = Path.Combine(Path.GetTempPath(), $"{Guid.NewGuid()}.csv");
+            await MiniExcel.SaveAsAsync(path, new[] {
+                new { c1 = "A1" ,c2 = (string)null},
+                new { c1 = (string)null ,c2 = (string)null},
+            });
+
+            using (var stream = File.OpenRead(path))
+            {
+                var rows = stream.Query<Test>(excelType: ExcelType.CSV).ToList();
+                Assert.Equal("A1", rows[0].c1);
+                Assert.Equal(string.Empty, rows[0].c2);
+                Assert.Equal(string.Empty, rows[1].c1);
+                Assert.Equal(string.Empty, rows[1].c2);
+            }
+
+            {
+                var rows = MiniExcel.Query<Test>(path, excelType: ExcelType.CSV).ToList();
+                Assert.Equal("A1", rows[0].c1);
+                Assert.Equal(string.Empty, rows[0].c2);
+                Assert.Equal(string.Empty, rows[1].c1);
+                Assert.Equal(string.Empty, rows[1].c2);
+            }
+
+            var config = new MiniExcelLibs.Csv.CsvConfiguration()
+            {
+                ReadEmptyStringAsNull = true
+            };
+            using (var stream = File.OpenRead(path))
+            {
+                var rows = stream.Query<Test>(excelType: ExcelType.CSV, configuration: config).ToList();
+                Assert.Equal("A1", rows[0].c1);
+                Assert.Null(rows[0].c2);
+                Assert.Null(rows[1].c1);
+                Assert.Null(rows[1].c2);
+            }
+
+            {
+                var rows = MiniExcel.Query<Test>(path, excelType: ExcelType.CSV, configuration: config).ToList();
+                Assert.Equal("A1", rows[0].c1);
+                Assert.Null(rows[0].c2);
+                Assert.Null(rows[1].c1);
+                Assert.Null(rows[1].c2);
+            }
+
+            File.Delete(path);
+        }
     }
 }