code: public static IMolecularFormula getMolecularFormula(String stringMF, IChemObjectBuilder builder) {
          return getMolecularFormula(stringMF, false, builder);
      }
docs: Construct an instance of IMolecularFormula, initialized with a molecular
  formula string. The string is immediately analyzed and a set of Nodes
  is built based on this analysis
  <p> The hydrogens must be implicit.
  
  @param  stringMF   The molecularFormula string
  @param builder a IChemObjectBuilder which is used to construct atoms
  @return            The filled IMolecularFormula
  @see               #getMolecularFormula(String,IMolecularFormula)