Fix messed up regex to account for empty string form (#10307)

* Fix messed up regex to account for empty string form

* Fix unit test

Author: rchiodo

news/2 Fixes/10204.md

@@ -0,0 +1 @@
+Fix empty variables to show an empty string in the Notebook/Interactive Window variable explorer.

src/client/datascience/jupyter/jupyterVariables.ts

@@ -32,7 +32,7 @@ import { JupyterDataRateLimitError } from './jupyterDataRateLimitError';
 // kernels will add the ansi encoding.
 const TypeRegex = /.*?\[.*?;31mType:.*?\[0m\s+(\w+)/;
 const ValueRegex = /.*?\[.*?;31mValue:.*?\[0m\s+(.*)/;
-const StringFormRegex = /.*?\[.*?;31mString form:.*?\[0m\s+([\s\S]+?)\n.*?\[.*?/;
+const StringFormRegex = /.*?\[.*?;31mString form:.*?\[0m\s*?([\s\S]+?)\n(.*\[.*;31m?)/;
 const DocStringRegex = /.*?\[.*?;31mDocstring:.*?\[0m\s+(.*)/;
 const CountRegex = /.*?\[.*?;31mLength:.*?\[0m\s+(.*)/;
 const ShapeRegex = /^\s+\[(\d+) rows x (\d+) columns\]/m;

src/test/datascience/jupyterVariables.unit.test.ts

@@ -302,7 +302,7 @@ This is equivalent to (real + imag*1j) where imag defaults to 0.
             truncated: true,
             count: 0,
             shape: '',
-            value: '(1+1j)',
+            value: ' (1+1j)',
             supportsDataExplorer: false
         };