RFR 8214971 : Replace use of string.equals("") with isEmpty()

[Pavel Rappo]

Roger, changes look good. On a side note, it's impressive how many cases we have
when we check for string not being null and empty. We should have had something
for that *internally* in the JDK. And it's a pity that `String.trim().isEmpty()`
not equivalent to `String.isBlank`. Seems to be a frequent case too.

> On 6 Dec 2018, at 20:04, Roger Riggs <Roger.Riggs at oracle.com> wrote:
> 
> Please review changing string.equals("") to string.isEmpty().
> isEmpty is preferred, performs better and is easier to optimize.
> 
> The change is a literal substitution in all files and only in these modules:
> 
>   java.base
>   java.logging
>   java.management
>   java.management.rmi
>   java.naming
>   java.net.http
>   java.prefs
>   java.rmi
>   java.scripting
>   java.sql
>   java.sql.rowset
>   java.xml
>   jdk.jartool
>   jdk.javadoc
>   jdk.jcmd
>   jdk.jconsole
>   jdk.management.agent
>   jdk.naming.dns
>   jdk.rmic
> 
> 
> Webrev:
> http://cr.openjdk.java.net/~rriggs/webrev-string-isempty-8214971-1/
> 
> Issue:
>   https://bugs.openjdk.java.net/browse/JDK-8214971
> 
> Thanks, Roger