Dashboards: Dashboard Crashes with Javascript exceptions when working with NULL variable values

### What happened? When a dashboard variable has NULL as one of it's possible values (For example as one of the results from an SQL query), It's very easy when interacting with the variable picker to encounter issues that cause a complete crash of the dashboard from a Javascript exception - As shown in this image  Actions that cause this crash include: 1. Clicking checkbox to select all variables (As opposed to the "All" option) 2. Entering various letters in the text filter field, including but possibly not limited to - "n","e","u","i","f". These only cause the crash if they are the first letters in the text box 3. Selecting the NULL option if variable is multi-select The specific error varies based on whichever of these I do, though they seem to be pretty similar. The text for the first crash is `TypeError: Cannot read properties of null (reading 'value') at G (https://****/public/build/3719.c065b2e146c4c8347d51.js:1:147070) at ne at ue (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:177215) at Wd.Component (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:292851) at Jt (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:138768) at div at om (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:333577) at h0 (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:333382) at Jt (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:138768) at div at https://****/public/build/3719.c065b2e146c4c8347d51.js:1:135436 at div at m (https://****/public/build/322.5df7dbfcd22d85fc7794.js:278:26159) at Jt (https://****/public/build/9636.b941a14f2c41910ad58c.js:39:138768) at div at div at st (https://****/public/build/322.5df7dbfcd22d85fc7794.js:275:243793) at div at div at Qe (https://****/public/build/322.5df7dbfcd22d85fc7794.js:275:242733) at Jt (https://****/public…