The method 'toLowerCase' was called on null.?

Question

I'm building a search feature on my flutter app to search for users from firebase.I know becasue i tried prininting the list that i populated.Here's the print statement [Instance of 'UserModel', Instance of 'UserModel', Instance of 'UserModel', Instance of 'UserModel']. I have 4 users on firebase and im able to retrieve all their data but when i type a letter in the search field I get this error.

    The following NoSuchMethodError was thrown building SearchScreen(dirty, state:
    _SearchScreenState#6b085):
    The method 'toLowerCase' was called on null.
    Receiver: null
    Tried calling: toLowerCase()

  I pasted the complete log and code on pastebin as stackoverflow  would let me post with the complete code.

https://pastebin.com/mFqvzh1v.I tried using ? operator

 String _getUsername = user.displayName?.toLowerCase();
  String _query = query?.toLowerCase();
  String _getName = user.username?.toLowerCase();
  bool matchesUsername = _getUsername.contains(_query)?? false;
  bool matchesName = _getName.contains(_query);

  return (matchesUsername || matchesName);

but im getting an error saying The method 'contains' was called on null. Receiver: null Tried calling: contains("m")

The relevant error-causing widget was: 
  SearchScreen file:///D:/fashow/lib/Timeline.dart:632:86
When the exception was thrown, this was the stack: 
#0      Object.noSuchMethod (dart:core-patch/object_patch.dart:51:5)
#1      _SearchScreenState.buildSuggestions.<anonymous closure> (package:fashow/Search_screen.dart:123:43)
#2      WhereIterator.moveNext (dart:_internal/iterable.dart:442:13)
#3      new List.from (dart:core-patch/array_patch.dart:50:19)
#4      new List.of (dart:core-patch/array_patch.dart:68:17)

"m" was the letter i typed on the keyboard

You should look at if all of the user models your are getting back have displayName set, as that would be my first guess, or query is null. — Garrett Barlocker
Please create a minimal, complete and verifiable example and post it directly into your question. — Christopher Moore
it is because, in theVariableYouExpectToBeAString.toLowerCase() the theVariableYouExpectToBeAString is null not a string — Yadu

ambiguous58 ambiguous58 · Accepted Answer · 2020-07-27T16:41:44

theVariableYouExpectToBeAString?.toLowerCase() ?? 'OtherStringJustInCase';

This will only avoid the exact error in your title. To find out the underlying problem set a breakpoint on this line and run in debug mode. The program will pause when it hits that line. Then you can inspect theVariableYouExpectToBeAString and see exactly what/where the issue is.

The method 'toLowerCase' was called on null.?

1 Answers