Refactoring: 30 small improvements/fixes

[carloscaldas]

Changes applied per file:

Road:

• Transformed instance variables into class variables: 1
• Added suffix to avoid loose of precision: 1
• Assigned variable never used: 1
• Removed redundant initialization: 1

PhyssimCalcLinkSpeedStats:

• Transformed static variables into constants: 3
• Transformed mutable object into immutable: 1
• Extracted method: 1
• Transformed instance variable into final instance variables: 5
• Removed redundant comments: 8
• Removed premature declaration: 1
• Transformed Boxed type into primitive type: 1

VehicleMilesTraveledAnalysis:

• Transformed instance variables into class variables: 1
• Added suffix to avoid loose of precision: 1
• Transformed instance variable into final instance variables: 2
• Avoid NullPointerException: 1
• Removed redundant comments: 1

#Relevant changes:

Bug fix:

Previous:

LinkedList<Double> gap = getGap();
if (gap == null) {
    gap = new LinkedList<>();
} else {
    gap.clear();
}

After:

if (gap == null) {
    gap = new LinkedList<>();
} else {
    gap.clear();
}

Comments: Assignment to the reference gap only updates the local variable that is not used

Avoid NPE:

Before:

this.vehicleTypes = vehicleTypes;

After:

this.vehicleTypes = vehicleTypes == null
    ? Set$.MODULE$.empty()
    : vehicleTypes;

Comments: The usage can lead to NPE. Other possible improvement would be to use Java Set instead of Scala Set since is a java class and no special feature from Scala collection is needed

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This change is 

[JustinPihony]

Minor nit - otherwise LGTM

[rajnikantsh]

LGTM