fix non-existent valueFrom path value throw panic error issue

Author: chihshenghuang

pkg/customresourcestate/registry_factory.go

@@ -278,6 +278,9 @@ func (c *compiledGauge) Values(v interface{}) (result []eachValue, errs []error)
 				onError(fmt.Errorf("[%d]: %w", i, err))
 				continue
 			}
+			if value == nil {
+				continue
+			}
 			addPathLabels(it, c.LabelFromPath(), value.Labels)
 			result = append(result, *value)
 		}
@@ -287,6 +290,9 @@ func (c *compiledGauge) Values(v interface{}) (result []eachValue, errs []error)
 			onError(err)
 			break
 		}
+		if value == nil {
+			break
+		}
 		addPathLabels(v, c.LabelFromPath(), value.Labels)
 		result = append(result, *value)
 	}

pkg/customresourcestate/registry_factory_test.go

@@ -210,6 +210,23 @@ func Test_values(t *testing.T) {
 		}, wantResult: nil, wantErrors: []error{
 			errors.New("[foo]: got nil while resolving path"),
 		}},
+		{name: "exist path but valueFrom path is non-existent single", each: &compiledGauge{
+			compiledCommon: compiledCommon{
+				path: mustCompilePath(t, "spec", "replicas"),
+			},
+			ValueFrom: mustCompilePath(t, "non-existent"),
+		}, wantResult: nil, wantErrors: nil,
+		},
+		{name: "exist path but valueFrom path non-existent array", each: &compiledGauge{
+			compiledCommon: compiledCommon{
+				path: mustCompilePath(t, "status", "condition_values"),
+				labelFromPath: map[string]valuePath{
+					"name": mustCompilePath(t, "name"),
+				},
+			},
+			ValueFrom: mustCompilePath(t, "non-existent"),
+		}, wantResult: nil, wantErrors: nil,
+		},
 		{name: "array", each: &compiledGauge{
 			compiledCommon: compiledCommon{
 				path: mustCompilePath(t, "status", "condition_values"),