title: angular build error: TypeError: Cannot read property 'line' of undefined
body: <p>I am suddenly facing build fail error for production.
  I am running this command:</p>
  
  <pre><code>ng build --prod
  </code></pre>
  
  <p>and getting following error:</p>
  
  <pre><code>D:\a\1\s\node_modules\clean-css\lib\reader\input-source-map-
  
  tracker.js:37
    if (originalPosition.line === null &amp;&amp; line &gt; 1 &amp;&amp; selectorFallbacks &gt; 0) {
                        ^
  TypeError: Cannot read property 'line' of undefined
      at originalPositionFor (D:\a\1\s\node_modules\clean-css\lib\reader\input-source-map-tracker.js:37:23)
      at originalMetadata (D:\a\1\s\node_modules\clean-css\lib\tokenizer\tokenize.js:486:43)
      at intoTokens (D:\a\1\s\node_modules\clean-css\lib\tokenizer\tokenize.js:435:68)
      at tokenize (D:\a\1\s\node_modules\clean-css\lib\tokenizer\tokenize.js:74:10)
      at fromStyles (D:\a\1\s\node_modules\clean-css\lib\reader\read-sources.js:147:12)
      at fromString (D:\a\1\s\node_modules\clean-css\lib\reader\read-sources.js:48:10)
      at doReadSources (D:\a\1\s\node_modules\clean-css\lib\reader\read-sources.js:33:12)
      at readSources (D:\a\1\s\node_modules\clean-css\lib\reader\read-sources.js:24:10)
      at D:\a\1\s\node_modules\clean-css\lib\clean.js:99:12
      at _combinedTickCallback (internal/process/next_tick.js:67:7)
      at process._tickCallback (internal/process/next_tick.js:98:9)
  Error: C:\Program Files\Git\bin\bash.exe failed with return code: 1
  </code></pre>
  
  <p>It used to work fine a few days ago but suddenly stopped working.
  Does any body have idea that why is this happening?</p>
  
  <p>(I am using angular cli version 1.6.7)</p>
  
  <p>Thanks in advance</p>