Prior to this commit, HtmlUnitRequestBuilder stored empty query
parameters declared without an equals sign as null (i.e., query
parameters such as 'error' in 'http://example.com/login?error').
This commit addresses this issue by ensuring that
HtmlUnitRequestBuilder treats all empty query parameter values as empty
strings. Consequently, query strings such as '?error' and '?error=' now
both result in 'error' being stored as an empty string.
Issue: SPR-13524
61a46db101