BelongsToMany Full Name Accessor

I have

    public function courses()
    {
        return $this->belongsToMany(Course::class);
    }

    public function courses()
    {
        return $this->belongsToMany(Course::class);
    }

    public function courses()
    {
        return $this->belongsToMany(Course::class);
    }

    public function courses()
    {
        return $this->belongsToMany(Course::class);
    }

in Course Model have

public function getFullNameAttribute()
    {
        return $this->department->name . ' ' . $this->course . ' ' . __('term');
    }

public function getFullNameAttribute()
    {
        return $this->department->name . ' ' . $this->course . ' ' . __('term');
    }

public function getFullNameAttribute()
    {
        return $this->department->name . ' ' . $this->course . ' ' . __('term');
    }

public function getFullNameAttribute()
    {
        return $this->department->name . ' ' . $this->course . ' ' . __('term');
    }

When call Tables\Columns\TextColumn::make('courses.full_name')

Getting empty field.

How can I solve this?