`ActiveGraph::Core::Query#return` throws error when passed a nil argument

[mrhardikjoshi]

Issue:
ActiveGraph::Core::Query#return method accepts variable length arguments, but fails when nil is present in this argument. the same issue is present with order clause

e.g.

core_query_obj.return('result_node_1', 'result_node_2').first  # works
core_query_obj.return(nil, 'result_node').first  # throws error

Stacktrace:

ArgumentError: Invalid argument for RETURN.  Full arguments: nil (ArgumentError)

          raise ArgumentError, message
                ^^^^^^^^^^^^^^^^^^^^^^
from activegraph-12.0.0.beta.5/lib/active_graph/core/query_clauses.rb:41:in 'ActiveGraph::Core::QueryClauses::Clause#value'
Caused by ActiveGraph::Core::QueryClauses::ArgError: ActiveGraph::Core::QueryClauses::ArgError
from activegraph-12.0.0.beta.5/lib/active_graph/core/query_clauses.rb:36:in 'ActiveGraph::Core::QueryClauses::Clause#value'

Expected Behavior:
Nil arguments should be filtered out (so that query.return(nil, 'result_node') is equivalent to query.return('result_node'))