Remove null Statements from logging output

[gitseti]

Problem or use case

Currently, the output in some log statements is too verbose because e.g every null assigned option is printed out.

As a user I want to see only the used options so I can quickly verify them.

2019-11-08 16:45:48: TRACE: SHELL: Command: ShellConnectCommand:
{host=broker.hivemq.com, port=1883, version=MQTT_5_0, identifier=mqtt-MQTT_5_0-
c929c2b5-a6cc-4e22-bd4e-3bf299e511aa, user='gitseti', keepAlive=null, 
cleanStart=null, useDefaultSsl=false, sslConfig=false, willTopic='null', 
willQos=null, willMessage='null', willRetain=null, 
willMessageExpiryInterval=null, willDelayInterval=null, 
willPayloadFormatIndicator=null, willContentType='null', 
willResponseTopic='null', willCorrelationData=null, willUserProperties=null, 
sessionExpiryInterval= null, userProperties=null, receiveMaximum=null, 
sendMaximum=null, maximumPacketSize=null, sendMaximumPacketSize=null, 
topicAliasMaximum=null, sendTopicAliasMaximum=null, 
requestProblemInformation=null, requestResponseInformation=null} 

Preferred solution or suggestions

Do not print null statements.
Clean up other logging relevant topics.