Add a ValueOr method to Optional

This allows easier use of the "the value in the Optional or this
default value I have" pattern.

src/lib/core/Optional.h

@@ -59,6 +59,17 @@ class Optional
         return mValue;
     }
 
+    /** Gets the current value of the optional if the optional has a value;
+        otherwise returns the provided default value. */
+    const T & ValueOr(const T & defaultValue) const
+    {
+        if (HasValue())
+        {
+            return mValue;
+        }
+        return defaultValue;
+    }
+
     /** Checks if the optional contains a value or not */
     bool HasValue() const { return mHasValue; }
 

src/protocols/echo/EchoClient.cpp

@@ -117,8 +117,7 @@ void EchoClient::OnMessageReceived(ExchangeContext * ec, const PacketHeader & pa
     // Call the registered OnEchoResponseReceived handler, if any.
     if (echoApp->OnEchoResponseReceived != nullptr)
     {
-        echoApp->OnEchoResponseReceived(packetHeader.GetSourceNodeId().HasValue() ? packetHeader.GetSourceNodeId().Value() : 0,
-                                        payload);
+        echoApp->OnEchoResponseReceived(packetHeader.GetSourceNodeId().ValueOr(0), payload);
     }
 
 exit:

src/transport/SecurePairingSession.cpp

@@ -59,8 +59,8 @@ CHIP_ERROR SecurePairingSession::Serialize(SecurePairingSessionSerialized & outp
 {
     CHIP_ERROR error = CHIP_NO_ERROR;
 
-    const NodeId localNodeId = (mLocalNodeId.HasValue()) ? mLocalNodeId.Value() : kUndefinedNodeId;
-    const NodeId peerNodeId  = (mPeerNodeId.HasValue()) ? mPeerNodeId.Value() : kUndefinedNodeId;
+    const NodeId localNodeId = mLocalNodeId.ValueOr(kUndefinedNodeId);
+    const NodeId peerNodeId  = mPeerNodeId.ValueOr(kUndefinedNodeId);
     VerifyOrExit(CanCastTo<uint16_t>(mKeLen), error = CHIP_ERROR_INTERNAL);
     VerifyOrExit(CanCastTo<uint64_t>(localNodeId), error = CHIP_ERROR_INTERNAL);
     VerifyOrExit(CanCastTo<uint64_t>(peerNodeId), error = CHIP_ERROR_INTERNAL);