Alerting: Fix ConditionsCmd No Data for "has no value" (#58634)

This commit fixes a bug where ConditionsCmd returns No Data even when
the condition checks for "has no value". It should return 1 with a nil
match.

pkg/expr/classic/classic_test.go

@@ -203,9 +203,8 @@ func TestConditionsCmd(t *testing.T) {
 			},
 		},
 		expected: func() mathexp.Results {
-			v := newNumber(nil)
-			// This seems incorrect
-			v.SetMeta([]EvalMatch{{}, {Metric: "NoData"}})
+			v := newNumber(ptr.Float64(1))
+			v.SetMeta([]EvalMatch{{Value: nil}})
 			return newResults(v)
 		},
 	}, {
@@ -226,9 +225,9 @@ func TestConditionsCmd(t *testing.T) {
 			},
 		},
 		expected: func() mathexp.Results {
-			v := newNumber(nil)
+			v := newNumber(ptr.Float64(1))
 			// This too seems incorrect, looks like we don't call the evaluator
-			v.SetMeta([]EvalMatch{{Metric: "NoData"}})
+			v.SetMeta([]EvalMatch{{Value: nil}})
 			return newResults(v)
 		},
 	}, {
@@ -251,9 +250,9 @@ func TestConditionsCmd(t *testing.T) {
 			},
 		},
 		expected: func() mathexp.Results {
-			v := newNumber(nil)
+			v := newNumber(ptr.Float64(1))
 			// This seems incorrect
-			v.SetMeta([]EvalMatch{{}, {Metric: "NoData"}})
+			v.SetMeta([]EvalMatch{{Value: nil}})
 			return newResults(v)
 		},
 	}, {