Fix IndexOutOfBoundsException for empty Window

Closes gh-775

Author: rstoyanchev

spring-graphql/src/main/java/org/springframework/graphql/data/pagination/ConnectionFieldTypeVisitor.java

@@ -217,6 +217,10 @@ private <T> Object adapt(@Nullable Object container) {
 			}
 
 			Collection<T> nodes = this.adapter.getContent(container);
+			if (nodes.isEmpty()) {
+				return EMPTY_CONNECTION;
+			}
+
 			int index = 0;
 			List<Edge<T>> edges = new ArrayList<>(nodes.size());
 			for (T node : nodes) {

spring-graphql/src/test/java/org/springframework/graphql/data/method/annotation/support/SchemaMappingPaginationTests.java

@@ -66,6 +66,23 @@ void forwardPagination() {
 								"}}}");
 	}
 
+	@Test // gh-775
+	void zeroResults() {
+
+		String document = BookSource.booksConnectionQuery("first:0, after:\"O_3\"");
+		Mono<ExecutionGraphQlResponse> response = graphQlService().execute(document);
+
+		ResponseHelper.forResponse(response).assertData("""
+				{"books":{\
+				"edges":[],\
+				"pageInfo":{\
+				"startCursor":null,\
+				"endCursor":null,\
+				"hasPreviousPage":false,\
+				"hasNextPage":false}}}"""
+		);
+	}
+
 	private TestExecutionGraphQlService graphQlService() {
 
 		ScrollPositionCursorStrategy cursorStrategy = new ScrollPositionCursorStrategy();