fixing initialization

Signed-off-by: Pedro Tanaka <pedro.tanaka@shopify.com>

pkg/dedup/iter.go

@@ -285,7 +285,7 @@ func newDedupSeriesIterator(a, b adjustableSeriesIterator) *dedupSeriesIterator
 		a:        a,
 		b:        b,
 		lastT:    math.MinInt64,
-		lastIter: nil,
+		lastIter: a,
 		useA:     true,
 		aval:     a.Next(),
 		bval:     b.Next(),
@@ -372,11 +372,11 @@ func (it *dedupSeriesIterator) Next() chunkenc.ValueType {
 
 func (it *dedupSeriesIterator) lastFloatVal() (float64, bool) {
 	if it.useA && it.aval == chunkenc.ValFloat {
-		_, v := it.a.At()
+		_, v := it.lastIter.At()
 		return v, true
 	}
 	if !it.useA && it.bval == chunkenc.ValFloat {
-		_, v := it.b.At()
+		_, v := it.lastIter.At()
 		return v, true
 	}
 	return 0, false

pkg/dedup/iter_test.go

@@ -623,6 +623,13 @@ func TestDedupSeriesIterator_NativeHistograms(t *testing.T) {
 		)
 		res := expandHistogramSeries(t, noopAdjustableSeriesIterator{it})
 		require.EqualValues(t, c.exp, res)
+
+		it = newDedupSeriesIterator(
+			noopAdjustableSeriesIterator{newMockedSeriesIterator(c.a)},
+			noopAdjustableSeriesIterator{testiters.NewHistogramIterator(c.b)},
+		)
+		res = expandHistogramSeries(t, noopAdjustableSeriesIterator{it})
+		require.EqualValues(t, c.exp, res)
 	}
 }