Opposite bpel validation rules in case WSDL messages with ommited parts. 
There are several use cases when bpel validation rules are inconsistent each other:

Invocation issue:
1. For <invoke>, request-response invocation requires both an inputVariable (or its equivalent <toPart> elements)
and an outputVariable (or its equivalent <fromPart> elements). And at the same time: "If a WSDL message definition does
not contain any parts, then the associated attributes, inputVariable or outputVariable, MAY be omitted, [SA00047] and
the <fromParts> or <toParts> construct MUST be omitted." Similar for the one way invocation. i.e. it is not required to
define inputVariable or outputVariable if the correspondent message parts are ommitted.

But in case inputVariable or outputVariable are ommited because the correspondent message parts are ommited the
validation error is appeared:
"
For <invoke>, request-response invocation requires both an inputVariable (or its equivalent <toPart> elements) and an
outputVariable (or its equivalent <fromPart> elements)"



receive/reply issues:
Similar for the receive(reply) inputVariable(outputVariable) is not required if the correspondent input(output) message
doesn't have any parts. But if inputVariable(outputVariable)is ommited then the following validation error is appeared:
"
For <receive> variable attribute (or its equivalent <fromPart> elements) must be specified. If a WSDL message definition
does not contain any parts, then the <fromParts> construct must be omitted.
"
("For <reply> variable attribute (or its equivalent <toPart> elements) must be specified. If a WSDL message definition
does not contain any parts, then the <toParts> construct must be omitted.
")


See also issue 109292.