Most and least frequent character

Write a function mostAndLeastFrequent(text) that finds the character that occurs most often in a string and the character that occurs least often.

• text is a string. It can be empty.
• Whitespace (spaces, tabs, line breaks) is not counted. Letters, digits and punctuation are counted.
• Case matters: 'a' and 'A' are different characters.
• Return an object { most, least }: most is the character with the highest frequency, least the character with the lowest frequency.
• If several characters have the same frequency, the one that first appears earlier in the text wins.
• If there are no characters to count (empty string or only whitespace), return { most: null, least: null }. Use null, not undefined.
• You can count with a map.