Fixed issue #7. Modified to check header column when it imported.

* Header column should not be null
* Header column should not be any c# keywords.

Assets/QuickSheet/ExcelPlugin/Editor/ExcelMachineEditor.cs

@@ -207,8 +207,14 @@ protected override void Import(bool reimport = false)
                 );
                 return;
             }
+            string error = string.Empty;
+            var titles = new ExcelQuery(path, sheet).GetTitle(0, ref error);
+            if (titles == null || !string.IsNullOrEmpty(error))
+            {
+                EditorUtility.DisplayDialog("Error", error, "OK");
+                return;
+            }
 
-            var titles = new ExcelQuery(path, sheet).GetTitle();
             List<string> titleList = titles.ToList();
 
             if (machine.HasHeadColumn() && reimport == false)

Assets/QuickSheet/ExcelPlugin/Editor/ExcelQuery.cs

@@ -45,11 +45,11 @@ public ExcelQuery(string path, string sheetName = "")
                         workbook = new HSSFWorkbook(fileStream);
                     else if (extension == "xlsx")
                     {
-#if UNITY_MAC
-                    throw new Exception("xlsx is not supported on OSX.");
-#else
+                    #if UNITY_EDITOR_OSX
+                        throw new Exception("xlsx is not supported on OSX.");
+                    #else
                         workbook = new XSSFWorkbook(fileStream);
-#endif
+                    #endif
                     }
                     else
                     {
@@ -200,24 +200,57 @@ public string[] GetSheetNames()
         }
 
         /// <summary>
-        /// Retrieves all first columns(aka. header) which are needed to determine type of each cell.
+        /// Retrieves all first columns(aka. header column) which are needed to determine each type of a cell.
         /// </summary>
-        public string[] GetTitle(int start = 0)
+        public string[] GetTitle(int start, ref string error)
         {
             List<string> result = new List<string>();
 
             IRow title = sheet.GetRow(start);
             if (title != null)
             {
                 for (int i = 0; i < title.LastCellNum; i++)
-                    result.Add(title.GetCell(i).StringCellValue);
+                {
+                    string value = title.GetCell(i).StringCellValue;
+                    if (string.IsNullOrEmpty(value))
+                    {
+                        error = string.Format(@"Empty column is found at {0}.", i);
+                        return null;
+                    }
+                    else
+                    {
+                        if (IsValidHeader(value))
+                            result.Add(value);
+                        else
+                        {
+                            error = string.Format(@"Error at column {0}, {1} is invalid name as header column.", i, value);
+                            return null;
+                        }
+                    }
+                }
 
                 return result.ToArray();
             }
-
+
+            error = string.Format(@"Empty row at {0}", start);
             return null;
         }
 
+        /// <summary>
+        /// Check the given header column has valid name which should not be any c# keywords.
+        /// </summary>
+        private bool IsValidHeader(string s)
+        {
+            // no case sensitive!
+            string comp = s.ToLower();
+
+            string found = Array.Find(Util.Keywords, x => x == comp);
+            if (string.IsNullOrEmpty(found))
+                return true;
+
+            return false;
+        }
+
         /// <summary>
         /// Convert type of cell value to its predefined type in the sheet's ScriptMachine setting file.
         /// </summary>

Assets/QuickSheet/Util/Util.cs

@@ -0,0 +1,21 @@
+using UnityEngine;
+using System.Collections;
+
+namespace UnityQuickSheet
+{
+    public class Util 
+    {
+        //all c# keywords.
+        public static string[] Keywords = new string[] {
+            "abstract", "as", "base", "bool", "break", "byte", "case", "catch", "char", "checked", 
+            "class", "const", "continue", "decimal", "default", "delegate", "do", "double", "else", "enum",
+            "event", "explicit", "extern", "false", "finally", "fixed", "float", "for", "foreach", "goto",
+            "if", "implicit", "in", "in", "int", "interface", "internal", "is", "lock", "long",
+            "namespace", "new", "null", "object", "operator", "out", "override", "params", "private", "protected",
+            "public", "readonly", "ref", "return", "sbyte", "sealed", "short", "sizeof", "stackalloc", "static", 
+            "string", "struct", "switch", "this", "throw", "true", "try", "typeof", "uint", "ulong", "unchecked", "unsafe",
+            "ushort", "using", "virtual", "void", "volatile", "while",
+        };
+
+    }
+}