Update dependency flutter_dotenv to v6

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
flutter_dotenv	dependencies	major	^5.1.0 → ^6.0.0

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Release Notes

java-james/flutter_dotenv (flutter_dotenv)

v6.0.1

Compare Source

• [fix] isEveryDefined() now throws NotInitializedError before load(), consistent with all other read APIs
• [fix] Replace assert() with explicit if/throw in getInt(), getDouble(), and getBool() so null-safety checks are enforced in release builds
• Error messages now include the variable name for easier debugging
• [fix] load(isOptional: true) no longer discards successfully loaded base file when an override file is missing or empty (fixes #​70, #​93, #​101, #​125)
• [fix] clean() now resets isInitialized to false, so accessing env after clean() correctly throws NotInitializedError
• [fix] Error classes (NotInitializedError, FileNotFoundError, EmptyEnvFileError) now include informative messages in toString() instead of the unhelpful Instance of 'ClassName' (fixes #​72, #​127; improves diagnostics for #​59, #​89)
• FileNotFoundError and EmptyEnvFileError now carry the filename when available

Note on error message improvements

NotInitializedError, FileNotFoundError, and EmptyEnvFileError now override toString() with actionable messages (e.g., FileNotFoundError: Environment file ".env" not found. Ensure the file exists and is listed under assets in pubspec.yaml.). This is not a breaking change — the class names and hierarchy are unchanged, so existing on FileNotFoundError catch clauses continue to work. FileNotFoundError now accepts an optional positional filename parameter, and EmptyEnvFileError accepts an optional named filename parameter; both default to null for backward compatibility.

Note on release-build behavior change

In debug mode, behavior is unchanged — AssertionError was thrown before, AssertionError is thrown now.

In release mode, calling getInt(), getDouble(), or getBool() with a missing variable and no fallback previously threw a TypeError (from the null-check operator !) because assert() was stripped. It now correctly throws AssertionError with a descriptive message. If your release-mode code catches on TypeError around these methods, update it to catch on AssertionError (or on Error) instead.

Breaking change: clean() now resets initialization state

Previously, calling clean() only cleared the env map but left isInitialized == true. Now it also sets isInitialized = false. Code that calls clean() and then immediately accesses dotenv.env without reloading will now throw NotInitializedError. The fix is to call load() or loadFromString() again after clean().

v6.0.0

Compare Source

• [feat] Allow passing in override .env files on init
• [feat] Load .env from a passed in string

Breaking changes

• Renamed: testLoad → loadFromString
  The method has been renamed to better reflect that it can be used outside of test environments.
  ⚠️ Update your code to call loadFromString() instead of testLoad().

• Behavior change: Empty file handling with isOptional = true
  Previously, if the env file was empty and isOptional was true, the method would throw.
  Now, in this case, it no longer throws and simply returns an empty env.

• Supported SDK range change: Dropped support for the pre release 2.12.0-0. Now supports 2.12.0 onwards.

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