[BUG] variable [soap] is not assigned if variable [continueRequestId] is not null

[peacexh]

Describe the bug In fuelsdk-1.6.0.jar, when calling the method retrieve() of the ETSoapObject class, if the variable continueRequestId has a value, nullPointException occurs because the variable soap is not assigned a value

[peacexh]

@vvitvits @svc-scm has the method can get more than 2500 pieces of data in In fuelsdk-1.6.0.jar(Java)