Merge pull request robinweser#215 from ahmaddehnavi/fix/plugins/flexb…

…oxIE/t.split_is_undefined

Fix/plugins/flexbox ie/t.split is undefined

modules/plugins/flexboxIE.js

@@ -24,7 +24,7 @@ const flexShorthandMappings = {
   unset: 'unset',
 }
 const isUnitlessNumber = /^\d+(\.\d+)?$/
-
+const logTag = 'inline-style-prefixer.flexboxIE plugin'
 export default function flexboxIE(
   property: string,
   value: any,
@@ -47,6 +47,22 @@ export default function flexboxIE(
       return
     }
 
+    if (typeof value === 'number' && value < 0) {
+      // ignore negative values;
+      console.warn(
+        `${logTag}: "flex: ${value}", negative values is not valid and will be ignored.`
+      )
+      return
+    }
+
+    if (!value.split) {
+      console.warn(
+        `${logTag}: "flex: ${value}", value format is not detected, it will be remain as is`
+      )
+      style.msFlex = value
+      return
+    }
+
     // The next thing we can look for is if there are multiple values.
     const flexValues = value.split(/\s/)
     // If we only have a single value that wasn't a positive unitless