Repository: angular
Issue: Empty expressions are not allowed
Labels: area: compiler,P4,compiler: parser

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# 🐞 bug report

### Affected Package
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<!-- ✍️edit: --> The issue is caused by package @angular/core (I believe?)


### Is this a regression?

<!-- Did this behavior use to work in the previous version? -->
<!-- ✍️--> Yes, the previous version in which this bug was not present was: ....

No idea, just noticed it

### Description

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Trying to add a `data` attribute to later on grab that reference into my Cypress test, I get `Empty expressions are not allowed`.   
I couldn't figure out why for a solid 45mn as I've done that pattern in plenty of other places. As I was doing this in an `ng-template` I thought maybe it was somehow related to that, or just a bug from the CLI. So I tried the classic `rm -rf node_modules && yarn` but nothing. The error was still here.

Turns out, I was trying to call my data attribute like this: `data-on-something` and apparently the `on` is being interpreted by Angular.

## 🔬 Minimal Reproduction
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Following is fine: `<div data-test>This one is fine</div>`

Following isn't fine: `<div data-on-test>This one is not fine</div>`

https://stackblitz.com/edit/angular-empty-expression-not-allowed-bug?file=src/app/app.component.html

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## 🔥 Exception or Error
<pre><code>Empty expressions are not allowed</code></pre>


## 🌍  Your Environment

**Angular Version:**
<pre><code>Angular CLI: 10.1.6
Node: 12.4.0
OS: linux x64

Angular: 10.1.5
... animations, common, compiler, compiler-cli, core, forms
... language-service, platform-browser, platform-browser-dynamic
... router
Ivy Workspace: <error>

Package                            Version
------------------------------------------------------------
@angular-devkit/architect          0.1001.6
@angular-devkit/build-angular      0.1001.6
@angular-devkit/build-ng-packagr   0.1001.6
@angular-devkit/build-optimizer    0.1001.6
@angular-devkit/core               10.0.6
@angular-devkit/schematics         10.0.6
@angular/cdk                       10.1.0
@angular/cli                       10.1.6
@angular/material                  10.1.0
@schematics/angular                10.1.6
@schematics/update                 0.1001.6
ng-packagr                         10.0.2
rxjs                               6.5.5
typescript                         4.0.3
webpack                            4.43.0</code></pre>

**Anything else relevant?**
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Nop