scrape tests: undo EmptyLabels change

Needs other code changes otherwise tests fail

Signed-off-by: Bryan Boreham <bjboreham@gmail.com>

scrape/manager_test.go

@@ -149,8 +149,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "no address",
 		},
 		// Address label missing, but added in relabelling.
@@ -242,8 +242,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "invalid label value for \"custom\": \"\\xbd\"",
 		},
 		// Invalid duration in interval label.
@@ -259,8 +259,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "error parsing scrape interval: not a valid duration string: \"2notseconds\"",
 		},
 		// Invalid duration in timeout label.
@@ -276,8 +276,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "error parsing scrape timeout: not a valid duration string: \"2notseconds\"",
 		},
 		// 0 interval in timeout label.
@@ -293,8 +293,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "scrape interval cannot be 0",
 		},
 		// 0 duration in timeout label.
@@ -310,8 +310,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "scrape timeout cannot be 0",
 		},
 		// Timeout less than interval.
@@ -328,8 +328,8 @@ func TestPopulateLabels(t *testing.T) {
 				ScrapeInterval: model.Duration(time.Second),
 				ScrapeTimeout:  model.Duration(time.Second),
 			},
-			res:     labels.EmptyLabels(),
-			resOrig: labels.EmptyLabels(),
+			res:     nil,
+			resOrig: nil,
 			err:     "scrape timeout cannot be greater than scrape interval (\"2s\" > \"1s\")",
 		},
 		// Don't attach default port.

scrape/scrape_test.go

@@ -1577,7 +1577,7 @@ func TestScrapeLoopAppendSampleLimit(t *testing.T) {
 		nil, nil, nil,
 		func(l labels.Labels) labels.Labels {
 			if l.Has("deleteme") {
-				return labels.EmptyLabels()
+				return nil
 			}
 			return l
 		},