fix(pwa): null check icon paths (#5087)

Author: janispritzkau

packages/@vue/cli-plugin-pwa/lib/HtmlPwaPlugin.js

@@ -81,22 +81,26 @@ module.exports = class HtmlPwaPlugin {
 
         const assetsVersionStr = assetsVersion ? `?v=${assetsVersion}` : ''
 
-        data.head.push(
-          // Favicons
-          makeTag('link', {
+        // Favicons
+        if (iconPaths.favicon32 != null) {
+          data.head.push(makeTag('link', {
             rel: 'icon',
             type: 'image/png',
             sizes: '32x32',
             href: getTagHref(publicPath, iconPaths.favicon32, assetsVersionStr)
-          }),
-          makeTag('link', {
+          }))
+        }
+        if (iconPaths.favicon16 != null) {
+          data.head.push(makeTag('link', {
             rel: 'icon',
             type: 'image/png',
             sizes: '16x16',
             href: getTagHref(publicPath, iconPaths.favicon16, assetsVersionStr)
-          }),
+          }))
+        }
 
-          // Add to home screen for Android and modern mobile browsers
+        // Add to home screen for Android and modern mobile browsers
+        data.head.push(
           makeTag('link', manifestCrossorigin
             ? {
               rel: 'manifest',
@@ -111,9 +115,11 @@ module.exports = class HtmlPwaPlugin {
           makeTag('meta', {
             name: 'theme-color',
             content: themeColor
-          }),
+          })
+        )
 
-          // Add to home screen for Safari on iOS
+        // Add to home screen for Safari on iOS
+        data.head.push(
           makeTag('meta', {
             name: 'apple-mobile-web-app-capable',
             content: appleMobileWebAppCapable
@@ -125,22 +131,30 @@ module.exports = class HtmlPwaPlugin {
           makeTag('meta', {
             name: 'apple-mobile-web-app-title',
             content: name
-          }),
-          makeTag('link', {
+          })
+        )
+        if (iconPaths.appleTouchIcon != null) {
+          data.head.push(makeTag('link', {
             rel: 'apple-touch-icon',
             href: getTagHref(publicPath, iconPaths.appleTouchIcon, assetsVersionStr)
-          }),
-          makeTag('link', {
+          }))
+        }
+        if (iconPaths.maskIcon != null) {
+          data.head.push(makeTag('link', {
             rel: 'mask-icon',
             href: getTagHref(publicPath, iconPaths.maskIcon, assetsVersionStr),
             color: themeColor
-          }),
+          }))
+        }
 
-          // Add to home screen for Windows
-          makeTag('meta', {
+        // Add to home screen for Windows
+        if (iconPaths.msTileImage != null) {
+          data.head.push(makeTag('meta', {
             name: 'msapplication-TileImage',
             content: getTagHref(publicPath, iconPaths.msTileImage, assetsVersionStr)
-          }),
+          }))
+        }
+        data.head.push(
           makeTag('meta', {
             name: 'msapplication-TileColor',
             content: msTileColor