[Tooltip] Fix useMemo dependency

[NMinhNguyen]

deepmerge supports null and undefined source,
no need to default to an empty object.

This is a follow-up to #19851.

That being said, if PopperProps is defined inline in user land, it would bust the cache all the time, so not sure how useful useMemo is. Unless we expect users to also memoise PopperProps 🤷‍♂️

• I have followed (at least) the PR section of the contributing guide.

[mui-pr-bot]

Details of bundle changes.

Comparing: b9dec27...ea4fa57

bundle	Size Change	Size	Gzip Change	Gzip
@material-ui/lab	▼ -21 B (-0.01% )	196 kB	▼ -16 B (-0.03% )	58.2 kB
@material-ui/core[umd]	▼ -21 B (-0.01% )	318 kB	▲ +13 B (+0.01% )	92.3 kB
@material-ui/core	▼ -21 B (-0.01% )	359 kB	▼ -11 B (-0.01% )	98.9 kB
docs.main	▼ -21 B (-0.00% )	601 kB	▼ -10 B (-0.01% )	195 kB
Tooltip	▼ -21 B (-0.02% )	102 kB	▼ -8 B (-0.02% )	32.5 kB
SpeedDialAction	▼ -21 B (-0.02% )	118 kB	▼ -6 B (-0.02% )	37.6 kB
@material-ui/styles	--	51.4 kB	--	15.4 kB
@material-ui/system	--	16.5 kB	--	4.32 kB
Alert	--	83.6 kB	--	26.4 kB
AlertTitle	--	64.5 kB	--	20.3 kB
AppBar	--	64.3 kB	--	20.2 kB
Autocomplete	--	132 kB	--	41.5 kB
Avatar	--	65.5 kB	--	20.7 kB
AvatarGroup	--	62.7 kB	--	19.7 kB
Backdrop	--	68.2 kB	--	21.1 kB
Badge	--	65.6 kB	--	20.4 kB
BottomNavigation	--	62.7 kB	--	19.7 kB
BottomNavigationAction	--	75.8 kB	--	24 kB
Box	--	72.2 kB	--	21.9 kB
Breadcrumbs	--	80.6 kB	--	25.4 kB
Button	--	80 kB	--	24.6 kB
ButtonBase	--	74.3 kB	--	23.4 kB
ButtonGroup	--	83.4 kB	--	25.6 kB
Card	--	63.2 kB	--	19.8 kB
CardActionArea	--	75.3 kB	--	23.8 kB
CardActions	--	62.4 kB	--	19.6 kB
CardContent	--	62.3 kB	--	19.5 kB
CardHeader	--	65.4 kB	--	20.6 kB
CardMedia	--	62.7 kB	--	19.7 kB
Checkbox	--	83.1 kB	--	26.3 kB
Chip	--	82.8 kB	--	25.4 kB
CircularProgress	--	64.4 kB	--	20.3 kB
ClickAwayListener	--	3.84 kB	--	1.54 kB
Collapse	--	68.3 kB	--	21.2 kB
colorManipulator	--	3.88 kB	--	1.52 kB
Container	--	63.5 kB	--	19.9 kB
CssBaseline	--	62.3 kB	--	19.6 kB
Dialog	--	83.2 kB	--	25.9 kB
DialogActions	--	62.4 kB	--	19.6 kB
DialogContent	--	62.5 kB	--	19.6 kB
DialogContentText	--	64.4 kB	--	20.2 kB
DialogTitle	--	64.6 kB	--	20.3 kB
Divider	--	63 kB	--	19.8 kB
docs.landing	--	56.6 kB	--	15.6 kB
Drawer	--	84.9 kB	--	25.9 kB
ExpansionPanel	--	72.6 kB	--	22.7 kB
ExpansionPanelActions	--	62.4 kB	--	19.6 kB
ExpansionPanelDetails	--	62.3 kB	--	19.5 kB
ExpansionPanelSummary	--	78.3 kB	--	24.8 kB
Fab	--	77.1 kB	--	24.1 kB
Fade	--	23.6 kB	--	8.01 kB
FilledInput	--	73.9 kB	--	23 kB
FormControl	--	64.7 kB	--	20.2 kB
FormControlLabel	--	65.8 kB	--	20.7 kB
FormGroup	--	62.3 kB	--	19.5 kB
FormHelperText	--	63.7 kB	--	20 kB
FormLabel	--	63.8 kB	--	19.8 kB
Grid	--	65.4 kB	--	20.5 kB
GridList	--	62.8 kB	--	19.7 kB
GridListTile	--	64 kB	--	20.1 kB
GridListTileBar	--	63.5 kB	--	19.9 kB
Grow	--	24.2 kB	--	8.22 kB
Hidden	--	66.3 kB	--	20.8 kB
Icon	--	63.1 kB	--	19.8 kB
IconButton	--	76.4 kB	--	23.9 kB
Input	--	72.9 kB	--	22.8 kB
InputAdornment	--	65.4 kB	--	20.6 kB
InputBase	--	71 kB	--	22.3 kB
InputLabel	--	65.6 kB	--	20.5 kB
LinearProgress	--	65.6 kB	--	20.5 kB
Link	--	66.9 kB	--	21.1 kB
List	--	62.7 kB	--	19.6 kB
ListItem	--	77.3 kB	--	24.3 kB
ListItemAvatar	--	62.4 kB	--	19.6 kB
ListItemIcon	--	62.5 kB	--	19.6 kB
ListItemSecondaryAction	--	62.3 kB	--	19.5 kB
ListItemText	--	65.3 kB	--	20.5 kB
ListSubheader	--	63.1 kB	--	19.8 kB
Menu	--	88.8 kB	--	27.5 kB
MenuItem	--	78.4 kB	--	24.6 kB
MenuList	--	66.3 kB	--	20.8 kB
MobileStepper	--	68.1 kB	--	21.4 kB
Modal	--	14.3 kB	--	5.03 kB
NativeSelect	--	77.1 kB	--	24.4 kB
NoSsr	--	2.17 kB	--	1.03 kB
OutlinedInput	--	74.9 kB	--	23.4 kB
Pagination	--	85.3 kB	--	26.3 kB
PaginationItem	--	81 kB	--	25 kB
Paper	--	62.7 kB	--	19.6 kB
Popover	--	83.2 kB	--	25.8 kB
Popper	--	28.8 kB	--	10.3 kB
Portal	--	2.87 kB	--	1.29 kB
Radio	--	84.1 kB	--	26.6 kB
RadioGroup	--	64.9 kB	--	20.2 kB
Rating	--	70.7 kB	--	22.7 kB
RootRef	--	4.21 kB	--	1.63 kB
ScopedCssBaseline	--	63.1 kB	--	19.9 kB
Select	--	116 kB	--	34.7 kB
Skeleton	--	63.3 kB	--	20 kB
Slide	--	25.6 kB	--	8.74 kB
Slider	--	76.9 kB	--	24.2 kB
Snackbar	--	75.6 kB	--	23.7 kB
SnackbarContent	--	63.8 kB	--	20.1 kB
SpeedDial	--	86.4 kB	--	27.3 kB
SpeedDialIcon	--	64.9 kB	--	20.3 kB
Step	--	63 kB	--	19.8 kB
StepButton	--	82.5 kB	--	26.2 kB
StepConnector	--	63 kB	--	19.8 kB
StepContent	--	69.5 kB	--	21.8 kB
StepIcon	--	64.9 kB	--	20.3 kB
StepLabel	--	68.9 kB	--	21.7 kB
Stepper	--	65.2 kB	--	20.6 kB
styles/createMuiTheme	--	16.6 kB	--	5.85 kB
SvgIcon	--	63.4 kB	--	19.8 kB
SwipeableDrawer	--	92.3 kB	--	28.9 kB
Switch	--	82.3 kB	--	26 kB
Tab	--	76.6 kB	--	24.3 kB
Table	--	62.9 kB	--	19.7 kB
TableBody	--	62.4 kB	--	19.5 kB
TableCell	--	64.3 kB	--	20.3 kB
TableContainer	--	62.3 kB	--	19.5 kB
TableFooter	--	62.4 kB	--	19.5 kB
TableHead	--	62.4 kB	--	19.5 kB
TablePagination	--	143 kB	--	42 kB
TableRow	--	62.8 kB	--	19.7 kB
TableSortLabel	--	77.6 kB	--	24.4 kB
Tabs	--	85.5 kB	--	27.2 kB
TextareaAutosize	--	5.19 kB	--	2.17 kB
TextField	--	125 kB	--	36.7 kB
ToggleButton	--	76.4 kB	--	24.2 kB
ToggleButtonGroup	--	63.5 kB	--	20 kB
Toolbar	--	62.7 kB	--	19.7 kB
TreeItem	--	75.5 kB	--	23.9 kB
TreeView	--	69.2 kB	--	21.7 kB
Typography	--	64 kB	--	20 kB
useAutocomplete	--	14.7 kB	--	5.33 kB
useMediaQuery	--	2.56 kB	--	1.06 kB
Zoom	--	23.6 kB	--	8.13 kB

Generated by 🚫 dangerJS against ea4fa57

[oliviertassinari]

I doubt we can write a test for this, unfortunately.
https://github.com/mui-org/material-ui/blob/b9dec2780203e37148d87788f727c668d9019581/packages/material-ui/src/Tooltip/Tooltip.test.js#L506

[NMinhNguyen]

I doubt we can write a test for this, unfortunately.

Strictly speaking, I could with mocks (or Enzyme and .props() - we’re trying to move away from it though) but I’m not sure it’s worth the effort? Actually I’m not sure how mocking is done in this environment, but it’s relatively easy with Jest 🙂

[oliviertassinari]

Thanks for the patch