java.lang.NumberFormatException: For input string: "" (Error when running `sbt test`)

I got this strange error when running "sbt test" on my Mac OS X(10.12.3) with Play 2.3.x, Scala (2.10.x). Java version on my local is java version "1.8.0_131".

I would really appreciate if someone could give me a quick pointer on the cause of this?

Error stack trace looks something like

[error]    NumberFormatException: : For input string: ""  (ProxyUtils.java:159)
[error] com.ning.http.util.ProxyUtils.createProxyServerSelector(ProxyUtils.java:159)
[error] com.ning.http.client.AsyncHttpClientConfig$Builder.build(AsyncHttpClientConfig.java:1132)
[error] play.api.libs.ws.ning.NingAsyncHttpClientConfigBuilder.build(NingAsyncHttpClientConfigBuilder.scala:37)
[error] play.api.libs.ws.ning.NingWSAPI.buildAsyncClientConfig(NingWS.scala:563)
[error] play.api.libs.ws.ning.NingWSAPI.newClient(NingWS.scala:520)
[error] play.api.libs.ws.ning.NingWSAPI$$anonfun$client$1.apply(NingWS.scala:543)
[error] play.api.libs.ws.ning.NingWSAPI$$anonfun$client$1.apply(NingWS.scala:540)
[error] play.api.libs.ws.ning.NingWSAPI.client(NingWS.scala:538)
[error] play.api.libs.ws.ning.NingWSAPI.url(NingWS.scala:553)
[error] play.api.libs.ws.WS$.url(WS.scala:129)