Welcome.js

import { PropTypes } from 'prop-types';
import React, { Component } from 'react';
import { View, Text, StyleSheet, Image, TouchableOpacity } from 'react-native';
// import { StackNavigator } from 'react-navigation';

// import SignUp from './SignUp';

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
  },
  imagePic: {
    width: 250,
    height: 250,
  },
  WelcomeText: {
    color: '#707071',
    width: 300,
    textAlign: 'center',
    fontSize: 20,
  },
  buttonWrapper: {
    flexDirection: 'row',
    justifyContent: 'space-between',
  },
  buttonContainer: {
    backgroundColor: '#38def3',
    width: 120,
    padding: 10,
    alignItems: 'center',
    margin: 20,
    borderRadius: 6,
  },
  buttonText: {
    color: '#fff',
    fontSize: 20,
    textAlign: 'center',
  },
});

class Welcome extends Component {
  static PropTypes = {
    navigation: PropTypes.object,
  };

  componentWillMount() {
    // functions
    handlePressLogin = () => {
      this.props.navigation.navigate('Login');   //the error this line : "Navigation is missing in props validation
    };
    handlePressSignUp = () => {
      this.props.navigation.navigate('SignUp'); // same error here too
    };
  }

  render() {
    // const { navigate } = this.props.navigation;
    return (
      <View style={styles.container}>
        <Text style={styles.WelcomeText}>Secure Your Future with a Click</Text>
        <Image style={styles.imagePic} source={require('../../app/images/SplashIcon.png')} />

        <View style={styles.buttonWrapper}>
          <TouchableOpacity style={styles.buttonContainer}>
            <Text onPress={() => this.handlePressLogin()} style={styles.buttonText}>
              Login
            </Text>
          </TouchableOpacity>

          <TouchableOpacity style={styles.buttonContainer}>
            <Text onPress={() => this.handlePressSignUp()} style={styles.buttonText}>
              Sign Up
            </Text>
          </TouchableOpacity>
        </View>
      </View>
    );
  }
}

export default Welcome;

It should be static propTypes = {...} (lower case p)