Disallow ERC20._transfer from the zero address.

contracts/mocks/ERC20Mock.sol

@@ -20,6 +20,10 @@ contract ERC20Mock is ERC20 {
         _burnFrom(account, amount);
     }
 
+    function transferInternal(address from, address to, uint256 value) public {
+        _transfer(from, to, value);
+    }
+
     function approveInternal(address owner, address spender, uint256 value) public {
         _approve(owner, spender, value);
     }

test/token/ERC20/ERC20.behavior.js

@@ -190,6 +190,28 @@ function shouldBehaveLikeERC20Transfer (errorPrefix, from, to, balance, transfer
         });
       });
     });
+
+    describe('when the sender transfers zero tokens', function () {
+      const amount = new BN('0');
+
+      it('transfers the requested amount', async function () {
+        await transfer.call(this, from, to, amount);
+
+        (await this.token.balanceOf(from)).should.be.bignumber.equal(balance);
+
+        (await this.token.balanceOf(to)).should.be.bignumber.equal('0');
+      });
+
+      it('emits a transfer event', async function () {
+        const { logs } = await transfer.call(this, from, to, amount);
+
+        expectEvent.inLogs(logs, 'Transfer', {
+          from,
+          to,
+          value: amount,
+        });
+      });
+    });
   });
 
   describe('when the recipient is the zero address', function () {
@@ -283,5 +305,6 @@ function shouldBehaveLikeERC20Approve (errorPrefix, owner, spender, supply, appr
 
 module.exports = {
   shouldBehaveLikeERC20,
+  shouldBehaveLikeERC20Transfer,
   shouldBehaveLikeERC20Approve,
 };

test/token/ERC20/ERC20.test.js

@@ -3,6 +3,7 @@ const { ZERO_ADDRESS } = constants;
 
 const {
   shouldBehaveLikeERC20,
+  shouldBehaveLikeERC20Transfer,
   shouldBehaveLikeERC20Approve,
 } = require('./ERC20.behavior');
 
@@ -330,6 +331,34 @@ contract('ERC20', function ([_, initialHolder, recipient, anotherAccount]) {
     });
   });
 
+  describe('_transfer', function () {
+    shouldBehaveLikeERC20Approve('ERC20', initialHolder, recipient, initialSupply, function (owner, spender, amount) {
+      return this.token.approveInternal(owner, spender, amount);
+    });
+
+    describe('when the owner is the zero address', function () {
+      it('reverts', async function () {
+        await shouldFail.reverting.withMessage(this.token.approveInternal(ZERO_ADDRESS, recipient, initialSupply),
+          'ERC20: approve from the zero address'
+        );
+      });
+    });
+  });
+
+  describe('_transfer', function () {
+    shouldBehaveLikeERC20Transfer('ERC20', initialHolder, recipient, initialSupply, function (from, to, amount) {
+      return this.token.transferInternal(from, to, amount);
+    });
+
+    describe('when the sender is the zero address', function () {
+      it('reverts', async function () {
+        await shouldFail.reverting.withMessage(this.token.transferInternal(ZERO_ADDRESS, recipient, initialSupply),
+          'ERC20: transfer from the zero address'
+        );
+      });
+    });
+  });
+
   describe('_approve', function () {
     shouldBehaveLikeERC20Approve('ERC20', initialHolder, recipient, initialSupply, function (owner, spender, amount) {
       return this.token.approveInternal(owner, spender, amount);