Remove unnecessary error condition

Failure match ${x.y.z} in ${x.y.z.q} should not be an error, it should
simply result in no values.

rule/context.go

@@ -243,10 +243,6 @@ func (c *Context) extractValues(v variable, resolvedList []resolvedObject) error
 		}
 	}
 
-	if len(vals) == 0 {
-		return errors.Errorf("no values of %s have key %s", v.prev().segmentName, v.segment)
-	}
-
 	c.values[v.segmentName] = vals
 	c.values[v.segment] = vals // this is the shortcut ${properties}, instead of ${x.y.properties}
 

rule/context_test.go

@@ -152,6 +152,48 @@ func TestContextResolve(t *testing.T) {
 			}`,
 		},
 		expectedValue: []string{"a", "b", "c", "d", "e"},
+	}, {
+		testName: "traverse many ist objects no results",
+		varName:  "${submission.foo.bar.rhubarb}",
+		fetcher: map[string]string{
+			submissionURI: `{
+				"foo": [
+					"http:/example.org/foo/1",
+					"http:/example.org/foo/2"
+				] 
+			}`,
+			"http:/example.org/foo/1": `{
+				"bar": [
+					"http:/example.org/bar/1",
+					"http:/example.org/bar/2"
+				]
+			}`,
+			"http:/example.org/foo/2": `{
+				"bar": [
+					"http:/example.org/bar/1",
+					"http:/example.org/bar/3"
+				]
+			}`,
+			"http:/example.org/bar/1": `{
+				"nope": [
+					"a",
+					"b"
+				]
+			}`,
+			"http:/example.org/bar/2": `{
+				"nope": [
+					"b",
+					"c"
+				]
+			}`,
+			"http:/example.org/bar/3": `{
+				"nope": [
+					"d",
+					"e"
+				]
+			}`,
+		},
+		expectedValue: []string{},
 	}}
 
 	for _, c := range cases {