code: public synchronized Operation namespaces(@Nullable final Map<String, String> namespaces) {
          this.namespaces = namespaces == null ? this.inheritedNamespaces : Data.newNamespaceMap(
                  namespaces, this.inheritedNamespaces);
          return this;
      }
docs: Sets the optional namespaces for this operation. Supplied namespaces overrides the
  namespaces inherited from the {@code Session}. Passing null will remove any namespace map
  previously set on the operation.
  
  @param namespaces
  the namespace map overriding session namespaces; null to reset
  @return this operation object for call chaining