private void visit(Expression<?> expr, QueryMetadata context) {
        if (expr != null) {
            expr.accept(this, context);
        }
    }
Copies {@code ParameterExpression} bindings from subexpressions to {@link QueryMetadata} in the context

@author tiwe
querydsl-core/src/main/java/com/querydsl/core/types/ParamsVisitor.java