hello , I'm new with arduino and I was trying to a project for mine! it was about connecting two arduino with i2c , keypad connected to master and lcd connected to slave! but after hours of working on it (was testing it in proteus), I managed to solve (some how ) it but the real issue is that LCD keep trping "black rectangles"(char 255) when i'm AFK and i tried to put if to remove that its keep typing empty characters. it keeps typing till i click on a button then it type that number and again type that stuff right after that. like this image

can you help me??

master code is :

#include <Keypad.h>
#include <Keypad_I2C.h>
#include<Wire.h>                             //Library for I2C Communication functions
char data;
const byte ROWS = 4; //four rows
const byte COLS = 3; //three columns
char keys[ROWS][COLS] = {
  {'1','2','3'},
  {'4','5','6'},
  {'7','8','9'},
  {'*','0','#'}
};
byte rowPins[ROWS] = {5, 4, 3, 2}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {8, 7, 6}; //connect to the column pinouts of the keypad
Keypad mykeypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
void setup()
{
  Serial.begin(9600); 
  Wire.begin();
}
void loop()
{
  unsigned char customkey = mykeypad.getKey();
  Wire.beginTransmission(4);
  if(customkey >= 0){
    Wire.write(customkey);
  }
  Wire.endTransmission(); 
  delay(50);
}

and slave is :

#include <Wire.h>
#include<LiquidCrystal.h>  
const int rs = 12, en = 11, d4 = 5, d5 = 4, d6 = 3, d7 = 2;
LiquidCrystal lcd(rs, en, d4, d5, d6, d7);       //Define LCD Module Pins (RS,EN,D4,D5,D6,D7)
void setup()
{
  Serial.begin(9600);
  Wire.begin(4);
  Wire.onReceive(receiveEvent); 
  lcd.begin(16, 2);
  lcd.print(0);
}



void receiveEvent(int numbytes)
{
} 

void loop(){
  char num = Wire.read(); 
  if (num!=char(255)){
    lcd.print(num);
  }
  delay(30);
}