requireSpaceBeforeKeywords: correct keywords check

Fixes #2135

Author: markelog

lib/rules/require-space-before-keywords.js

@@ -55,9 +55,11 @@ module.exports.prototype = {
             excludedKeywords = keywords.allExcept;
         }
 
-        keywords = defaultKeywords.filter(function(keyword) {
-            return (excludedKeywords.indexOf(keyword) === -1);
-        });
+        if (!Array.isArray(keywords)) {
+            keywords = defaultKeywords.filter(function(keyword) {
+                return (excludedKeywords.indexOf(keyword) === -1);
+            });
+        }
 
         this._keywords = keywords;
     },

test/specs/rules/require-space-before-keywords.js

@@ -121,4 +121,12 @@ describe('rules/require-space-before-keywords', function() {
         expect(errors).to.have.one.validation.error.from('requireSpaceBeforeKeywords');
         expect(errors.explainError(error)).to.have.string('Missing space before "function" keyword');
     });
+
+    it('should ignore keywords that is not mentioned in the config list (#2135)', function() {
+        checker.configure({ requireSpaceBeforeKeywords: [] });
+
+        expect(
+            checker.checkString('if (typeof value !== "function") {}')
+        ).to.have.no.errors();
+    });
 });