biblatex.tex

% See https://tex.stackexchange.com/questions/469555/unicode-u301-error-in-biblatex-but-not-in-main-text-i

\DeclareDatafieldSet{setall}{
  \member[datatype=literal]
  \member[datatype=name]
  \member[field=journal]% journal is special since it is
                        % actually journaltitle
}

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map[overwrite, foreach={setall}]{
      % \`{\i}
      \step[fieldsource=\regexp{$MAPLOOP},
            match=\regexp{\x{0131}\x{0300}},
            replace=\regexp{\x{00EC}}]
      % \'{\i}
      \step[fieldsource=\regexp{$MAPLOOP},
            match=\regexp{\x{0131}\x{0301}},
            replace=\regexp{\x{00ED}}]
      % \^{\i}
      \step[fieldsource=\regexp{$MAPLOOP},
            match=\regexp{\x{0131}\x{0302}},
            replace=\regexp{\x{00EE}}]
      % \"{\i}
      \step[fieldsource=\regexp{$MAPLOOP},
            match=\regexp{\x{0131}\x{0308}},
            replace=\regexp{\x{00EF}}]
    }
  }
}