fix for index out of range [0] in codegen.LowerTitle when input is empty (#1069)

Co-authored-by: Kyle Conroy <kyle@conroy.org>

Author: eivindr

internal/codegen/utils.go

@@ -6,6 +6,10 @@ import (
 )
 
 func LowerTitle(s string) string {
+	if s == "" {
+		return s
+	}
+
 	a := []rune(s)
 	a[0] = unicode.ToLower(a[0])
 	return string(a)

internal/codegen/utils_test.go

@@ -0,0 +1,28 @@
+package codegen
+
+import (
+	"testing"
+)
+
+func TestLowerTitle(t *testing.T) {
+
+	// empty
+	if LowerTitle("") != "" {
+		t.Fatal("expected empty title to remain empty")
+	}
+
+	// all lowercase
+	if LowerTitle("lowercase") != "lowercase" {
+		t.Fatal("expected no changes when input is all lowercase")
+	}
+
+	// all uppercase
+	if LowerTitle("UPPERCASE") != "uPPERCASE" {
+		t.Fatal("expected first rune to be lower when input is all uppercase")
+	}
+
+	// Title Case
+	if LowerTitle("Title Case") != "title Case" {
+		t.Fatal("expected first rune to be lower when input is Title Case")
+	}
+}