charts: Fix error handling if gvRenderData() returns an error

If libgvc was not built properly or is running against incorrectly versioned
plugins, gvRenderData() can fail and return a null string. Ensure libvaladoc
handles this correctly.

https://bugzilla.gnome.org/show_bug.cgi?id=711590

2 files changed, 8 insertions, 5 deletions

diff --git a/src/libvaladoc/charts/chart.vala b/src/libvaladoc/charts/chart.vala
index 03dab30f7..a6307d7ff 100644
--- a/src/libvaladoc/charts/chart.vala
+++ b/src/libvaladoc/charts/chart.vala
@@ -52,13 +52,14 @@ public class Valadoc.Charts.Chart : Api.Visitor {
 		context.render (graph, file_type, file);
 	}
 
-	public uint8[] write_buffer (string file_type) {
+	public uint8[]? write_buffer (string file_type) {
 		if (context == null) {
 			context = factory.create_context (graph);
 		}
 
-		uint8[] data;
+		uint8[]? data;
 
+		/* This will return null in data if it fails. */
 		context.render_data (graph, file_type, out data);
 		return data;
 	}
diff --git a/src/libvaladoc/html/htmlmarkupwriter.vala b/src/libvaladoc/html/htmlmarkupwriter.vala
index 113f0c6f1..15ed9efd1 100644
--- a/src/libvaladoc/html/htmlmarkupwriter.vala
+++ b/src/libvaladoc/html/htmlmarkupwriter.vala
@@ -44,9 +44,11 @@ public class Valadoc.Html.MarkupWriter : Valadoc.MarkupWriter {
 	}
 
 	public MarkupWriter add_usemap (Charts.Chart chart) {
-		string buf = (string) chart.write_buffer ("cmapx");
-		raw_text ("\n");
-		raw_text (buf);
+		string? buf = (string?) chart.write_buffer ("cmapx");
+		if (buf != null) {
+			raw_text ("\n");
+			raw_text ((!) buf);
+		}
 
 		return this;
 	}