# "sexp" variable contents at top of Arguments#consume in lib/compiler/nodes.rb ~ line 1146
# initial args sexp: [[], [:b], nil, [:block, [:lasgn, :a, [:lasgn, :b, [:hash]]]]]
# return value at bottom of that method: (@name added to inspect for clarity)
# updated args sexp: [[], [:b], nil, [#<Compiler:lasgn @name=>:a>]]

# based on the following input program:
def foo(a = b = {})
end

# What ends up happening is that "@mapped_defaults" uses :a as its key to this lasgn, rather than :b as it should
# When that default is needed in bytecode.rb, it is looked up via :b and returns nil