Argument #1 ($values) must be of type array, null given Laravel 9

I have 3 Models in My Laravel App like Employee , Salary and Title. Employee Model one to Many Relationship with both Salary and Title Models. Now I need update data using EmployeeController updateEmployee function using this function I need update some time all 3 tables tada also.
EmployeeController

public function updateEmployee(Request $request, $id) {
        $employee = Employee::find($id);
        $title = $employee->titles()->update($request->title);

        $salary = $employee->salaries()->update($request->salary);

        if(is_null($employee)) {
            return response()->json(['message' => 'Employee not found'], 404);
        }
        $employee->update($request->all());
        
        return response($employee, 200);
    
    }

and my api route is following

Route::put('updateEmployee/{id}','AppHttpControllersEmployeeController@updateEmployee');

Employee Model

public function titles(): HasMany
{
    return $this->hasMany(Title::class, 'emp_no');
}

public function salaries(): HasMany
{
    return $this->hasMany(Salary::class, 'emp_no');
}

Salary Model

public function employee(): BelongsTo
{
    return $this->belongsTo(Employee::class, 'emp_no');
}

Title Model

public function employee(): BelongsTo
{
    return $this->belongsTo(Employee::class, 'emp_no');
}

but when I try update using postman I got following error message
TypeError: IlluminateDatabaseEloquentBuilder::update(): Argument #1 ($values) must be of type array, null given, called in F:2023code2023apivendorlaravelframeworksrcIlluminateSupportTraitsForwardsCalls.php on line 23 in file F:2023code2023apivendorlaravelframeworksrcIlluminateDatabaseEloquentBuilder.php on line 1009
how could I fix this problem?