Make confgraph and graph in general more resilient to bad input

1 files changed, 5 insertions, 0 deletions

diff --git a/graph.go b/graph.go
index 955abbd..1604d06 100644
--- a/graph.go
+++ b/graph.go
@@ -1,6 +1,7 @@
 package bookpipeline
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"path/filepath"
@@ -61,6 +62,10 @@ func Graph(confs map[string]*Conf, bookname string, w io.Writer) error {
 	}
 	sort.Slice(graphconf, func(i, j int) bool { return graphconf[i].Pgnum < graphconf[j].Pgnum })
 
+	if len(graphconf) == 0 {
+		return errors.New("No valid confidences")
+	}
+
 	// Create main xvalues and yvalues, annotations and ticks
 	var xvalues, yvalues []float64
 	var annotations []chart.Value2