fixed issue #63 relating to writing of NULL values

Author: iliaal

tests/056.phpt

@@ -34,7 +34,7 @@ float(434324)
 string(6) "string"
 string(8) "fsdfasDF"
 string(4) "NULL"
-string(0) ""
+NULL
 string(6) "string"
 string(0) ""
 OK

tests/write_read_row_bug.phpt

@@ -0,0 +1,33 @@
+--TEST--
+A bug with using readRow/writeRow combination to handle NULL values
+--SKIPIF--
+<?php if (!extension_loaded("excel")) print "skip"; ?>
+--FILE--
+<?php 
+$book = new ExcelBook();
+$ws = $book->addSheet("foo");
+
+$row = array('a', 'b', 'c', NULL, 1, 2, 3);
+var_dump(
+	$ws->writeRow(1, $row),
+	$ws->readRow(1)
+);
+?>
+--EXPECT--
+bool(true)
+array(7) {
+  [0]=>
+  string(1) "a"
+  [1]=>
+  string(1) "b"
+  [2]=>
+  string(1) "c"
+  [3]=>
+  NULL
+  [4]=>
+  float(1)
+  [5]=>
+  float(2)
+  [6]=>
+  float(3)
+}