fix: trim fileExtensions entries and reject blank-only arrays

The ignore and ignoreFiles options have always been trimmed; fileExtensions
was not. A leading/trailing space produced a glob like **/*. scss  which
matched nothing.

Author: XhmikosR

index.js

@@ -113,9 +113,14 @@ function parseOptions(opts) {
   let extensions = options.fileExtensions;
 
   extensions = Array.isArray(extensions) ? extensions : [extensions];
-  // Replace possible fullstop prefix
-  extensions = extensions.map(ext => ext.startsWith('.') ? ext.slice(1) : ext);
-  extensions = extensions.filter(ext => ext.length > 0);
+  // Trim, strip a leading dot, and drop blanks
+  extensions = extensions
+    .map(extension => {
+      const trimmed = extension.trim();
+      return trimmed.startsWith('.') ? trimmed.slice(1) : trimmed;
+    })
+    .filter(Boolean);
+
   if (extensions.length === 0) {
     throw new TypeError('`fileExtensions` must contain at least one non-empty extension');
   }

tests/api.test.js

@@ -68,6 +68,16 @@ test('throws TypeError when fileExtensions is an empty array', () => {
   }, TypeError);
 });
 
+test('throws TypeError when fileExtensions contains only blank strings', () => {
+  assert.throws(() => {
+    find(fixturesDir, { fileExtensions: ['  '] });
+  }, TypeError);
+});
+
+test('fileExtensions with surrounding whitespace is trimmed and works', () => {
+  const result = find(fixturesDir, { fileExtensions: [' scss '] });
+  assert.equal(result.total, 2);
+});
 
 test('find accepts null opts without throwing', () => {
   const result = find(fixturesDir, null);