[PATCH v1 4/9] MdePkg: Add definition for NULL GUID

["Sami Mujawar" <sami.mujawar@arm.com>]

Bugzilla: 3668 (https://bugzilla.tianocore.org/show_bug.cgi?id=3668)

Some PCDs e.g. PcdCpuRngSupportedAlgorithm are defined as GUIDs and
may be initialised as NULL (all zeros) by default. Therefore, define
a NULL GUID (128 bit zeros), so that it can be used for comparison
using CompareGuid().

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---
 MdePkg/Include/Guid/NullGuid.h | 21 ++++++++++++++++++++
 MdePkg/MdePkg.dec              |  6 ++++++
 2 files changed, 27 insertions(+)

diff --git a/MdePkg/Include/Guid/NullGuid.h b/MdePkg/Include/Guid/NullGuid.h
new file mode 100644
index 0000000000000000000000000000000000000000..e44a92c7863f0573ce10d6d98e4a67e3d63f5743
--- /dev/null
+++ b/MdePkg/Include/Guid/NullGuid.h
@@ -0,0 +1,21 @@
+/** @file
+  Definition of a NULL GUID.
+
+  Copyright (c) 2021, Arm Limited. All rights reserved.<BR>
+
+  SPDX-License-Identifier: BSD-2-Clause-Patent
+
+**/
+
+#ifndef NULL_GUID_H_
+#define NULL_GUID_H_
+
+// {00000000-0000-0000-0000-000000000000}
+#define NULL_GUID \
+  { \
+    0x00000000, 0x0000, 0x0000, {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 } \
+  }
+
+extern EFI_GUID gNullGuid;
+
+#endif // NULL_GUID_H_
diff --git a/MdePkg/MdePkg.dec b/MdePkg/MdePkg.dec
index 492c3c3fd83e632dbf902bd8093b7d5e62597433..dcdccf2b68b58536b84f1c360ef048ca8f2f1690 100644
--- a/MdePkg/MdePkg.dec
+++ b/MdePkg/MdePkg.dec
@@ -828,6 +828,12 @@ [Guids]
   #
   gLinuxEfiInitrdMediaGuid       = {0x5568e427, 0x68fc, 0x4f3d, {0xac, 0x74, 0xca, 0x55, 0x52, 0x31, 0xcc, 0x68}}
 
+  #
+  # Definition of a NULL GUID
+  #
+  ## Include/Guid/NullGuid.h
+  gNullGuid = { 0x00000000, 0x0000, 0x0000, { 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00 }}
+
 [Guids.IA32, Guids.X64]
   ## Include/Guid/Cper.h
   gEfiIa32X64ErrorTypeCacheCheckGuid = { 0xA55701F5, 0xE3EF, 0x43de, { 0xAC, 0x72, 0x24, 0x9B, 0x57, 0x3F, 0xAD, 0x2C }}
-- 
'Guid(CE165669-3EF3-493F-B85D-6190EE5B9759)'