Refactoring local variable usage

[sergkop]

While working on #1146 I've found a number of inconsistencies in the usage of local variables and method arguments. Here is a bit of refactoring.

Type of change

• Refactoring

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes