fix: emit empty strings through valueStream instead of throwing missingData

Source/Experimental/DataBinding/RiveViewModelInstanceData.mm

@@ -87,11 +87,8 @@ - (instancetype)initWithData:(rive::CommandQueue::ViewModelInstanceData)data
                 break;
             case rive::DataType::string:
             case rive::DataType::enumType:
-                if (!data.stringValue.empty())
-                {
-                    _stringValue = [NSString
-                        stringWithUTF8String:data.stringValue.c_str()];
-                }
+                _stringValue = [NSString
+                    stringWithUTF8String:data.stringValue.c_str()];
                 break;
             default:
                 // For other types, try stringValue if it's not empty

Tests/Experimental/DataBinding/ViewModelInstanceTests.swift

@@ -188,6 +188,61 @@ class ViewModelInstanceTests: XCTestCase {
         XCTAssertEqual(unsubscribeCall.requestID, requestID)
     }
 
+    @MainActor
+    func test_value_withEmptyStringProperty_returnsEmptyString() async throws {
+        let mockCommandQueue = MockCommandQueue()
+        var capturedObserver: ViewModelInstanceListener?
+
+        let viewModelInstance = makeViewModelInstance(mockCommandQueue: mockCommandQueue) { observer in
+            capturedObserver = observer
+        }
+
+        mockCommandQueue.stubRequestViewModelInstanceString { instanceHandle, path, requestID in
+            let mockData = MockRiveViewModelInstanceData(stringValue: "")
+            capturedObserver?.onViewModelDataReceived(instanceHandle, requestID: requestID, data: mockData)
+        }
+
+        let property = StringProperty(path: "test.path")
+        let value = try await viewModelInstance.value(of: property)
+
+        XCTAssertEqual(value, "")
+    }
+
+    @MainActor
+    func test_valueStream_withEmptyStringProperty_yieldsEmptyString() async throws {
+        let mockCommandQueue = MockCommandQueue()
+
+        let viewModelInstance = makeViewModelInstance(mockCommandQueue: mockCommandQueue)
+
+        let property = StringProperty(path: "test.path")
+        let stream = viewModelInstance.valueStream(of: property)
+
+        let subscribeCall = mockCommandQueue.subscribeToViewModelPropertyCalls[0]
+        let observer = mockCommandQueue.getObserver(for: 99)
+        let requestID = subscribeCall.requestID
+
+        let task = Task {
+            var values: [String] = []
+            for try await value in stream {
+                values.append(value)
+                if values.count >= 2 { break }
+            }
+            return values
+        }
+
+        let nonEmpty = MockRiveViewModelInstanceData(stringValue: "hello")
+        observer?.onViewModelDataReceived(99, requestID: requestID, data: nonEmpty)
+
+        let empty = MockRiveViewModelInstanceData(stringValue: "")
+        observer?.onViewModelDataReceived(99, requestID: requestID, data: empty)
+
+        let values = try await task.value
+
+        XCTAssertEqual(values.count, 2)
+        XCTAssertEqual(values[0], "hello")
+        XCTAssertEqual(values[1], "")
+    }
+
     // MARK: - Number
 
     @MainActor