diff --git a/packages/less/src/less-browser/utils.js b/packages/less/src/less-browser/utils.js
index 42a1b442e..039f1d595 100644
--- a/packages/less/src/less-browser/utils.js
+++ b/packages/less/src/less-browser/utils.js
@@ -9,7 +9,7 @@ export function extractId(href) {
 }
 
 export function addDataAttr(options, tag) {
-	if(!tag) return; // in case of tag is null or undefined
+    if (!tag) {return;} // in case of tag is null or undefined
     for (const opt in tag.dataset) {
         if (tag.dataset.hasOwnProperty(opt)) {
             if (opt === 'env' || opt === 'dumpLineNumbers' || opt === 'rootpath' || opt === 'errorReporting') {
diff --git a/packages/less/src/less/environment/environment.js b/packages/less/src/less/environment/environment.js
index 39de0d315..f7d65c6a1 100644
--- a/packages/less/src/less/environment/environment.js
+++ b/packages/less/src/less/environment/environment.js
@@ -30,7 +30,7 @@ class Environment {
         if (!filename) {
             logger.warn('getFileManager called with no filename.. Please report this issue. continuing.');
         }
-        if (currentDirectory == null) {
+        if (currentDirectory === undefined) {
             logger.warn('getFileManager called with null directory.. Please report this issue. continuing.');
         }
 
diff --git a/packages/less/src/less/functions/default.js b/packages/less/src/less/functions/default.js
index fc7fd63aa..61c14b9ac 100644
--- a/packages/less/src/less/functions/default.js
+++ b/packages/less/src/less/functions/default.js
@@ -1,4 +1,5 @@
 import Keyword from '../tree/keyword';
+import * as utils from '../utils';
 
 const defaultFunc = {
     eval: function () {
@@ -7,7 +8,7 @@ const defaultFunc = {
         if (e) {
             throw e;
         }
-        if (v != null) {
+        if (!utils.isNullOrUndefined(v)) {
             return v ? Keyword.True : Keyword.False;
         }
     },
diff --git a/packages/less/src/less/functions/math-helper.js b/packages/less/src/less/functions/math-helper.js
index ed6deaa75..b557875c5 100644
--- a/packages/less/src/less/functions/math-helper.js
+++ b/packages/less/src/less/functions/math-helper.js
@@ -4,7 +4,7 @@ const MathHelper = (fn, unit, n) => {
     if (!(n instanceof Dimension)) {
         throw { type: 'Argument', message: 'argument must be a number' };
     }
-    if (unit == null) {
+    if (unit === null) {
         unit = n.unit;
     } else {
         n = n.unify();
diff --git a/packages/less/src/less/parser/parser.js b/packages/less/src/less/parser/parser.js
index c7a65cb07..2b2799c62 100644
--- a/packages/less/src/less/parser/parser.js
+++ b/packages/less/src/less/parser/parser.js
@@ -581,7 +581,7 @@ const Parser = function Parser(context, imports, fileInfo) {
 
                     expectChar(')');
 
-                    return new(tree.URL)((value.value != null || 
+                    return new(tree.URL)((value.value !== undefined || 
                         value instanceof tree.Variable || 
                         value instanceof tree.Property) ?
                         value : new(tree.Anonymous)(value, index), index, fileInfo);
diff --git a/packages/less/src/less/tree/node.js b/packages/less/src/less/tree/node.js
index b40e30da9..4aadc261c 100644
--- a/packages/less/src/less/tree/node.js
+++ b/packages/less/src/less/tree/node.js
@@ -1,3 +1,5 @@
+import * as utils from '../utils';
+
 /**
  * The reason why Node is a class and other nodes simply do not extend
  * from Node (since we're transpiling) is due to this issue:
@@ -125,21 +127,21 @@ class Node {
 
     // Returns true if this node represents root of ast imported by reference
     blocksVisibility() {
-        if (this.visibilityBlocks == null) {
+        if (this.visibilityBlocks === undefined) {
             this.visibilityBlocks = 0;
         }
         return this.visibilityBlocks !== 0;
     }
 
     addVisibilityBlock() {
-        if (this.visibilityBlocks == null) {
+        if (this.visibilityBlocks === undefined) {
             this.visibilityBlocks = 0;
         }
         this.visibilityBlocks = this.visibilityBlocks + 1;
     }
 
     removeVisibilityBlock() {
-        if (this.visibilityBlocks == null) {
+        if (this.visibilityBlocks === undefined) {
             this.visibilityBlocks = 0;
         }
         this.visibilityBlocks = this.visibilityBlocks - 1;
diff --git a/packages/less/src/less/tree/quoted.js b/packages/less/src/less/tree/quoted.js
index d73c40ca6..7c96c0ecd 100644
--- a/packages/less/src/less/tree/quoted.js
+++ b/packages/less/src/less/tree/quoted.js
@@ -1,10 +1,11 @@
 import Node from './node';
 import Variable from './variable';
 import Property from './property';
+import * as utils from '../utils';
 
 
 const Quoted = function(str, content, escaped, index, currentFileInfo) {
-    this.escaped = (escaped == null) ? true : escaped;
+    this.escaped = (escaped === undefined) ? true : escaped;
     this.value = content || '';
     this.quote = str.charAt(0);
     this._index = index;
diff --git a/packages/less/src/less/tree/ruleset.js b/packages/less/src/less/tree/ruleset.js
index 22f68b75c..dfd044932 100644
--- a/packages/less/src/less/tree/ruleset.js
+++ b/packages/less/src/less/tree/ruleset.js
@@ -734,7 +734,7 @@ Ruleset.prototype = Object.assign(new Node(), {
                 // non parent reference elements just get added
                 if (el.value !== '&') {
                     const nestedSelector = findNestedSelector(el);
-                    if (nestedSelector != null) {
+                    if (nestedSelector !== null) {
                         // merge the current list of non parent selector elements
                         // on to the current list of selectors to add
                         mergeElementsOnToSelectors(currentElements, newSelectors);
diff --git a/packages/less/src/less/tree/selector.js b/packages/less/src/less/tree/selector.js
index a198a7740..d098cc2bc 100644
--- a/packages/less/src/less/tree/selector.js
+++ b/packages/less/src/less/tree/selector.js
@@ -1,6 +1,7 @@
 import Node from './node';
 import Element from './element';
 import LessError from '../less-error';
+import * as utils from '../utils';
 
 const Selector = function(elements, extendList, condition, index, currentFileInfo, visibilityInfo) {
     this.extendList = extendList;
@@ -33,7 +34,7 @@ Selector.prototype = Object.assign(new Node(), {
         elements = this.getElements(elements);
         const newSelector = new Selector(elements, extendList || this.extendList,
             null, this.getIndex(), this.fileInfo(), this.visibilityInfo());
-        newSelector.evaldCondition = (evaldCondition != null) ? evaldCondition : this.evaldCondition;
+        newSelector.evaldCondition = (!utils.isNullOrUndefined(evaldCondition)) ? evaldCondition : this.evaldCondition;
         newSelector.mediaEmpty = this.mediaEmpty;
         return newSelector;
     },
diff --git a/packages/less/src/less/utils.js b/packages/less/src/less/utils.js
index c0921b90d..b723ab2ac 100644
--- a/packages/less/src/less/utils.js
+++ b/packages/less/src/less/utils.js
@@ -119,4 +119,8 @@ export function flattenArray(arr, result = []) {
         }
     }
     return result;
+}
+
+export function isNullOrUndefined(val) {
+    return val === null || val === undefined
 }
\ No newline at end of file