No errors in editor: session does not support events

TypeScript Version: 2.8.0-dev.20180322 (works in 2.8.0-dev.20180321)

Search Terms:

Code

const x: number = "";

Expected behavior:

Shows the error.

Actual behavior:

From tsserver.log:

Info 78   [9:1:58.995] Session does not support events: ignored event: {"seq":0,"type":"event","event":"semanticDiag","body":{"file":"c:/Users/anhans/work/sample/ts/src/a.ts","diagnostics":[{"start":{"line":1,"offset":7},"end":{"line":1,"offset":8},"text":"Type '\"\"' is not assignable to type 'number'.","code":2322,"category":"error"}]}}

Works in the commit before #22591