check for the empty string

Summary:
Bug:

{F157985015}

Reviewed By: danielbuechele

Differential Revision: D15260689

fbshipit-source-id: c43cdc0fc0d3e624ad930af60a9c95996579acb6

src/plugins/logs/index.js

@@ -58,6 +58,9 @@ const Icon = styled(Glyph)({
 
 function getLineCount(str: string): number {
   let count = 1;
+  if (!(typeof str === 'string')) {
+    return 0;
+  }
   for (let i = 0; i < str.length; i++) {
     if (str[i] === '\n') {
       count++;