@Nullable
  public static PsiType getReturnType(List<? extends GrSignature> signatures) {
    if (signatures.size() == 1) {
      return signatures.get(0).getReturnType();
    }
    else if (signatures.size() > 1) {
      final PsiType type = signatures.get(0).getReturnType();
      if (type == null) return null;
      String firstType = type.getCanonicalText();
      for (int i = 1; i < signatures.size(); i++) {
        final PsiType _type = signatures.get(i).getReturnType();
        if (_type == null) return null;
        if (!firstType.equals(_type.getCanonicalText())) return null;
      }
      return type;
    }
    else {
      return null;
    }
  }
@Nullable
  public static PsiType getReturnType(List<? extends GrSignature> signatures)