User.Smart Null values for string return errors

I am trying to get information for GitHub users, namely email addresses. When using a User.Smart object, calling the email() and bio() functions fail with a ClassCastException shown below:

```
User.Smart user = new User.Smart(github.users().get(username));
System.out.println(user.email());
```

```
java.lang.ClassCastException: Cannot cast javax.json.JsonValue$1 to javax.json.JsonString
at java.lang.Class.cast(Class.java:3369)
at com.jcabi.github.SmartJson.value_aroundBody6(SmartJson.java:139)
at com.jcabi.github.SmartJson$AjcClosure7.run(SmartJson.java:1)
at org.aspectj.runtime.reflect.JoinPointImpl.proceed(JoinPointImpl.java:149)
at com.jcabi.aspects.aj.MethodLogger.wrap(MethodLogger.java:213)
at com.jcabi.aspects.aj.MethodLogger.ajc$inlineAccessMethod$com_jcabi_aspects_aj_MethodLogger$com_jcabi_aspects_aj_MethodLogger$wrap(MethodLogger.java:1)
at com.jcabi.aspects.aj.MethodLogger.wrapClass(MethodLogger.java:140)
at com.jcabi.github.SmartJson.value(SmartJson.java:116)
at com.jcabi.github.SmartJson.text_aroundBody0(SmartJson.java:79)
at com.jcabi.github.SmartJson$AjcClosure1.run(SmartJson.java:1)
at org.aspectj.runtime.reflect.JoinPointImpl.proceed(JoinPointImpl.java:149)
at com.jcabi.aspects.aj.MethodLogger.wrap(MethodLogger.java:213)
at com.jcabi.aspects.aj.MethodLogger.ajc$inlineAccessMethod$com_jcabi_aspects_aj_MethodLogger$com_jcabi_aspects_aj_MethodLogger$wrap(MethodLogger.java:1)
at com.jcabi.aspects.aj.MethodLogger.wrapClass(MethodLogger.java:140)
at com.jcabi.github.SmartJson.text(SmartJson.java:79)
at com.jcabi.github.User$Smart.email_aroundBody16(User.java:232)
at com.jcabi.github.User$Smart$AjcClosure17.run(User.java:1)
at org.aspectj.runtime.reflect.JoinPointImpl.proceed(JoinPointImpl.java:149)
at com.jcabi.aspects.aj.MethodLogger.wrap(MethodLogger.java:213)
at com.jcabi.aspects.aj.MethodLogger.ajc$inlineAccessMethod$com_jcabi_aspects_aj_MethodLogger$com_jcabi_aspects_aj_MethodLogger$wrap(MethodLogger.java:1)
at com.jcabi.aspects.aj.MethodLogger.wrapClass(MethodLogger.java:140)
at com.jcabi.github.User$Smart.email(User.java:232)
at com.chbrown13.tool_rec.Recommender.main(Recommender.java:196)
```