Fixing test when labels values are not found -> return nil instead of empty array

Signed-off-by: Alan Protasio <alanprot@gmail.com>

Author: alanprot

pkg/querier/blocks_store_queryable.go

@@ -345,7 +345,7 @@ func (q *blocksStoreQuerier) LabelNames(ctx context.Context, matchers ...*labels
 
 	var (
 		resMtx            sync.Mutex
-		resNameSet        = []string{}
+		resNameSet        []string
 		resWarnings       = annotations.Annotations(nil)
 		convertedMatchers = convertMatchersToLabelMatcher(matchers)
 	)
@@ -383,7 +383,7 @@ func (q *blocksStoreQuerier) LabelValues(ctx context.Context, name string, match
 	minT, maxT := q.minT, q.maxT
 
 	var (
-		resValueSets = []string{}
+		resValuesSet []string
 		resWarnings  = annotations.Annotations(nil)
 
 		resultMtx sync.Mutex
@@ -396,7 +396,7 @@ func (q *blocksStoreQuerier) LabelValues(ctx context.Context, name string, match
 		}
 
 		resultMtx.Lock()
-		resValueSets = strutil.MergeSlices(resValueSets, valueSets)
+		resValuesSet = strutil.MergeSlices(resValuesSet, valueSets)
 		resWarnings.Merge(warnings)
 		resultMtx.Unlock()
 
@@ -407,7 +407,7 @@ func (q *blocksStoreQuerier) LabelValues(ctx context.Context, name string, match
 		return nil, nil, err
 	}
 
-	return resValueSets, resWarnings, nil
+	return resValuesSet, resWarnings, nil
 }
 
 func (q *blocksStoreQuerier) Close() error {