key: fix panic when recursive value has missing target (#191)

key.go

@@ -147,10 +147,15 @@ func (k *Key) transformValue(val string) string {
 		noption := vr[2 : len(vr)-2]
 
 		// Search in the same section.
+		// If not found or found the key itself, then search again in default section.
 		nk, err := k.s.GetKey(noption)
 		if err != nil || k == nk {
-			// Search again in default section.
 			nk, _ = k.s.f.Section("").GetKey(noption)
+			if nk == nil {
+				// Stop when no results found in the default section,
+				// and returns the value as-is.
+				break
+			}
 		}
 
 		// Substitute by new value and take off leading '%(' and trailing ')s'.

key_test.go

@@ -551,7 +551,19 @@ NAME = %(NAME)s
 expires = %(expires)s`))
 		So(err, ShouldBeNil)
 		So(f, ShouldNotBeNil)
+
 		So(f.Section("package").Key("NAME").String(), ShouldEqual, "ini")
 		So(f.Section("package").Key("expires").String(), ShouldEqual, "yes")
 	})
+
+	Convey("Recursive value with no target found", t, func() {
+		f, err := ini.Load([]byte(`
+[foo]
+bar = %(missing)s
+`))
+		So(err, ShouldBeNil)
+		So(f, ShouldNotBeNil)
+
+		So(f.Section("foo").Key("bar").String(), ShouldEqual, "%(missing)s")
+	})
 }