Make argsKV more predictable

Fixes #932

args.go

@@ -361,7 +361,13 @@ func visitArgs(args []argsKV, f func(k, v []byte)) {
 func copyArgs(dst, src []argsKV) []argsKV {
 	if cap(dst) < len(src) {
 		tmp := make([]argsKV, len(src))
+		dst = dst[:cap(dst)] // copy all of dst.
 		copy(tmp, dst)
+		for i := len(dst); i < len(tmp); i++ {
+			// Make sure nothing is nil.
+			tmp[i].key = []byte{}
+			tmp[i].value = []byte{}
+		}
 		dst = tmp
 	}
 	n := len(src)
@@ -442,7 +448,9 @@ func allocArg(h []argsKV) ([]argsKV, *argsKV) {
 	if cap(h) > n {
 		h = h[:n+1]
 	} else {
-		h = append(h, argsKV{})
+		h = append(h, argsKV{
+			value: []byte{},
+		})
 	}
 	return h, &h[n]
 }

args_test.go

@@ -596,4 +596,28 @@ func TestArgsDeleteAll(t *testing.T) {
 	if a.Len() != 1 || a.Has("q1") {
 		t.Fatalf("Expected q1 arg to be completely deleted. Current Args: %s", a.String())
 	}
-}
+}
+
+func TestIssue932(t *testing.T) {
+	t.Parallel()
+	var a []argsKV
+
+	a = setArg(a, "t1", "ok", argsHasValue)
+	a = setArg(a, "t2", "", argsHasValue)
+	a = setArg(a, "t1", "", argsHasValue)
+	a = setArgBytes(a, s2b("t3"), []byte{}, argsHasValue)
+	a = setArgBytes(a, s2b("t4"), nil, argsHasValue)
+
+	if peekArgStr(a, "t1") == nil {
+		t.Error("nil not expected for t1")
+	}
+	if peekArgStr(a, "t2") == nil {
+		t.Error("nil not expected for t2")
+	}
+	if peekArgStr(a, "t3") == nil {
+		t.Error("nil not expected for t3")
+	}
+	if peekArgStr(a, "t4") != nil {
+		t.Error("nil expected for t4")
+	}
+}