Unresolved attribute reference

In this code:

class Utility:

  def Enquote(s,quoteChar='"'):

    if quoteChar == '"':

      s = s.replace(quoteChar,quoteChar + quoteChar)

    return quoteChar + s + quoteChar

... PyCharm is highlighting "replace" with:

Unresolved attribute reference 'replace' for class 'Utility'

... even though the code runs fine.  Two questions: is this a PyCharm bug, and regardless ... can I supress this error?

As an aside, I'm a Python noob and initially wrote this with "import string" at the top of the file and the replace(s,quoteChar,quoteChar + quoteChar) syntax, and that also was reported the same way.