diff --git a/lib/widgets/code_block.dart b/lib/widgets/code_block.dart
index 19402646ba..12c0ad28b1 100644
--- a/lib/widgets/code_block.dart
+++ b/lib/widgets/code_block.dart
@@ -477,73 +477,73 @@ class CodeBlockTextStyles {
     };
   }
 
-  CodeBlockTextStyles lerp(CodeBlockTextStyles? other, double t) {
-    if (identical(this, other)) return this;
+  static CodeBlockTextStyles lerp(CodeBlockTextStyles a, CodeBlockTextStyles b, double t) {
+    if (identical(a, b)) return a;
 
     return CodeBlockTextStyles._(
-      plain: TextStyle.lerp(plain, other?.plain, t)!,
-      hll: TextStyle.lerp(_hll, other?._hll, t)!,
-      c: TextStyle.lerp(_c, other?._c, t)!,
-      err: TextStyle.lerp(_err, other?._err, t)!,
-      k: TextStyle.lerp(_k, other?._k, t)!,
-      o: TextStyle.lerp(_o, other?._o, t)!,
-      cm: TextStyle.lerp(_cm, other?._cm, t)!,
-      cp: TextStyle.lerp(_cp, other?._cp, t)!,
-      c1: TextStyle.lerp(_c1, other?._c1, t)!,
-      cs: TextStyle.lerp(_cs, other?._cs, t)!,
-      gd: TextStyle.lerp(_gd, other?._gd, t)!,
-      ge: TextStyle.lerp(_ge, other?._ge, t)!,
-      gr: TextStyle.lerp(_gr, other?._gr, t)!,
-      gh: TextStyle.lerp(_gh, other?._gh, t)!,
-      gi: TextStyle.lerp(_gi, other?._gi, t)!,
-      go: TextStyle.lerp(_go, other?._go, t)!,
-      gp: TextStyle.lerp(_gp, other?._gp, t)!,
-      gs: TextStyle.lerp(_gs, other?._gs, t)!,
-      gu: TextStyle.lerp(_gu, other?._gu, t)!,
-      gt: TextStyle.lerp(_gt, other?._gt, t)!,
-      kc: TextStyle.lerp(_kc, other?._kc, t)!,
-      kd: TextStyle.lerp(_kd, other?._kd, t)!,
-      kn: TextStyle.lerp(_kn, other?._kn, t)!,
-      kp: TextStyle.lerp(_kp, other?._kp, t)!,
-      kr: TextStyle.lerp(_kr, other?._kr, t)!,
-      kt: TextStyle.lerp(_kt, other?._kt, t)!,
-      m: TextStyle.lerp(_m, other?._m, t)!,
-      s: TextStyle.lerp(_s, other?._s, t)!,
-      na: TextStyle.lerp(_na, other?._na, t)!,
-      nb: TextStyle.lerp(_nb, other?._nb, t)!,
-      nc: TextStyle.lerp(_nc, other?._nc, t)!,
-      no: TextStyle.lerp(_no, other?._no, t)!,
-      nd: TextStyle.lerp(_nd, other?._nd, t)!,
-      ni: TextStyle.lerp(_ni, other?._ni, t)!,
-      ne: TextStyle.lerp(_ne, other?._ne, t)!,
-      nf: TextStyle.lerp(_nf, other?._nf, t)!,
-      nl: TextStyle.lerp(_nl, other?._nl, t)!,
-      nn: TextStyle.lerp(_nn, other?._nn, t)!,
-      nt: TextStyle.lerp(_nt, other?._nt, t)!,
-      nv: TextStyle.lerp(_nv, other?._nv, t)!,
-      nx: TextStyle.lerp(_nx, other?._nx, t)!,
-      ow: TextStyle.lerp(_ow, other?._ow, t)!,
-      w: TextStyle.lerp(_w, other?._w, t)!,
-      mf: TextStyle.lerp(_mf, other?._mf, t)!,
-      mh: TextStyle.lerp(_mh, other?._mh, t)!,
-      mi: TextStyle.lerp(_mi, other?._mi, t)!,
-      mo: TextStyle.lerp(_mo, other?._mo, t)!,
-      sb: TextStyle.lerp(_sb, other?._sb, t)!,
-      sc: TextStyle.lerp(_sc, other?._sc, t)!,
-      sd: TextStyle.lerp(_sd, other?._sd, t)!,
-      s2: TextStyle.lerp(_s2, other?._s2, t)!,
-      se: TextStyle.lerp(_se, other?._se, t)!,
-      sh: TextStyle.lerp(_sh, other?._sh, t)!,
-      si: TextStyle.lerp(_si, other?._si, t)!,
-      sx: TextStyle.lerp(_sx, other?._sx, t)!,
-      sr: TextStyle.lerp(_sr, other?._sr, t)!,
-      s1: TextStyle.lerp(_s1, other?._s1, t)!,
-      ss: TextStyle.lerp(_ss, other?._ss, t)!,
-      bp: TextStyle.lerp(_bp, other?._bp, t)!,
-      vc: TextStyle.lerp(_vc, other?._vc, t)!,
-      vg: TextStyle.lerp(_vg, other?._vg, t)!,
-      vi: TextStyle.lerp(_vi, other?._vi, t)!,
-      il: TextStyle.lerp(_il, other?._il, t)!,
+      plain: TextStyle.lerp(a.plain, b.plain, t)!,
+      hll: TextStyle.lerp(a._hll, b._hll, t)!,
+      c: TextStyle.lerp(a._c, b._c, t)!,
+      err: TextStyle.lerp(a._err, b._err, t)!,
+      k: TextStyle.lerp(a._k, b._k, t)!,
+      o: TextStyle.lerp(a._o, b._o, t)!,
+      cm: TextStyle.lerp(a._cm, b._cm, t)!,
+      cp: TextStyle.lerp(a._cp, b._cp, t)!,
+      c1: TextStyle.lerp(a._c1, b._c1, t)!,
+      cs: TextStyle.lerp(a._cs, b._cs, t)!,
+      gd: TextStyle.lerp(a._gd, b._gd, t)!,
+      ge: TextStyle.lerp(a._ge, b._ge, t)!,
+      gr: TextStyle.lerp(a._gr, b._gr, t)!,
+      gh: TextStyle.lerp(a._gh, b._gh, t)!,
+      gi: TextStyle.lerp(a._gi, b._gi, t)!,
+      go: TextStyle.lerp(a._go, b._go, t)!,
+      gp: TextStyle.lerp(a._gp, b._gp, t)!,
+      gs: TextStyle.lerp(a._gs, b._gs, t)!,
+      gu: TextStyle.lerp(a._gu, b._gu, t)!,
+      gt: TextStyle.lerp(a._gt, b._gt, t)!,
+      kc: TextStyle.lerp(a._kc, b._kc, t)!,
+      kd: TextStyle.lerp(a._kd, b._kd, t)!,
+      kn: TextStyle.lerp(a._kn, b._kn, t)!,
+      kp: TextStyle.lerp(a._kp, b._kp, t)!,
+      kr: TextStyle.lerp(a._kr, b._kr, t)!,
+      kt: TextStyle.lerp(a._kt, b._kt, t)!,
+      m: TextStyle.lerp(a._m, b._m, t)!,
+      s: TextStyle.lerp(a._s, b._s, t)!,
+      na: TextStyle.lerp(a._na, b._na, t)!,
+      nb: TextStyle.lerp(a._nb, b._nb, t)!,
+      nc: TextStyle.lerp(a._nc, b._nc, t)!,
+      no: TextStyle.lerp(a._no, b._no, t)!,
+      nd: TextStyle.lerp(a._nd, b._nd, t)!,
+      ni: TextStyle.lerp(a._ni, b._ni, t)!,
+      ne: TextStyle.lerp(a._ne, b._ne, t)!,
+      nf: TextStyle.lerp(a._nf, b._nf, t)!,
+      nl: TextStyle.lerp(a._nl, b._nl, t)!,
+      nn: TextStyle.lerp(a._nn, b._nn, t)!,
+      nt: TextStyle.lerp(a._nt, b._nt, t)!,
+      nv: TextStyle.lerp(a._nv, b._nv, t)!,
+      nx: TextStyle.lerp(a._nx, b._nx, t)!,
+      ow: TextStyle.lerp(a._ow, b._ow, t)!,
+      w: TextStyle.lerp(a._w, b._w, t)!,
+      mf: TextStyle.lerp(a._mf, b._mf, t)!,
+      mh: TextStyle.lerp(a._mh, b._mh, t)!,
+      mi: TextStyle.lerp(a._mi, b._mi, t)!,
+      mo: TextStyle.lerp(a._mo, b._mo, t)!,
+      sb: TextStyle.lerp(a._sb, b._sb, t)!,
+      sc: TextStyle.lerp(a._sc, b._sc, t)!,
+      sd: TextStyle.lerp(a._sd, b._sd, t)!,
+      s2: TextStyle.lerp(a._s2, b._s2, t)!,
+      se: TextStyle.lerp(a._se, b._se, t)!,
+      sh: TextStyle.lerp(a._sh, b._sh, t)!,
+      si: TextStyle.lerp(a._si, b._si, t)!,
+      sx: TextStyle.lerp(a._sx, b._sx, t)!,
+      sr: TextStyle.lerp(a._sr, b._sr, t)!,
+      s1: TextStyle.lerp(a._s1, b._s1, t)!,
+      ss: TextStyle.lerp(a._ss, b._ss, t)!,
+      bp: TextStyle.lerp(a._bp, b._bp, t)!,
+      vc: TextStyle.lerp(a._vc, b._vc, t)!,
+      vg: TextStyle.lerp(a._vg, b._vg, t)!,
+      vi: TextStyle.lerp(a._vi, b._vi, t)!,
+      il: TextStyle.lerp(a._il, b._il, t)!,
     );
   }
 }
diff --git a/lib/widgets/content.dart b/lib/widgets/content.dart
index 4ac92abaa3..04dfa15a90 100644
--- a/lib/widgets/content.dart
+++ b/lib/widgets/content.dart
@@ -99,15 +99,15 @@ class ContentTheme extends ThemeExtension<ContentTheme> {
   }
 
   @override
-  ContentTheme lerp(ContentTheme? other, double t) {
+  ContentTheme lerp(ContentTheme other, double t) {
     if (identical(this, other)) {
       return this;
     }
     return ContentTheme._(
-      textStylePlainParagraph: TextStyle.lerp(textStylePlainParagraph, other?.textStylePlainParagraph, t)!,
-      codeBlockTextStyles: codeBlockTextStyles.lerp(other?.codeBlockTextStyles, t),
-      textStyleError: TextStyle.lerp(textStyleError, other?.textStyleError, t)!,
-      textStyleErrorCode: TextStyle.lerp(textStyleErrorCode, other?.textStyleErrorCode, t)!,
+      textStylePlainParagraph: TextStyle.lerp(textStylePlainParagraph, other.textStylePlainParagraph, t)!,
+      codeBlockTextStyles: CodeBlockTextStyles.lerp(codeBlockTextStyles, other.codeBlockTextStyles, t),
+      textStyleError: TextStyle.lerp(textStyleError, other.textStyleError, t)!,
+      textStyleErrorCode: TextStyle.lerp(textStyleErrorCode, other.textStyleErrorCode, t)!,
     );
   }
 }
diff --git a/lib/widgets/stream_colors.dart b/lib/widgets/stream_colors.dart
index 9435b9cb1e..5c9a23c800 100644
--- a/lib/widgets/stream_colors.dart
+++ b/lib/widgets/stream_colors.dart
@@ -23,27 +23,25 @@ abstract class StreamColorSwatches {
 
   StreamColorSwatch _computeForBaseColor(int base);
 
-  /// Gives a [StreamColorSwatches], lerped to [other] at [t].
+  /// Gives a [StreamColorSwatches], lerped between [a] and [b] at [t].
   ///
-  /// If [this] and [other] are [identical], returns [this].
+  /// If [a] and [b] are [identical], returns [this].
   ///
   /// Else returns an instance whose [forBaseColor] will call
-  /// [this.forBaseColor] and [other.forBaseColor]
+  /// [a.forBaseColor] and [b.forBaseColor]
   /// and return [StreamColorSwatch.lerp]'s result on those.
   /// This computation is cached on the instance
   /// in order to save work building [t]'s animation frame when there are
   /// multiple UI elements using the same [subscription.color].
-  StreamColorSwatches lerp(StreamColorSwatches? other, double t) {
+  static StreamColorSwatches lerp(StreamColorSwatches a, StreamColorSwatches b, double t) {
     // This short-circuit helps when [a] and [b]
     // are both [StreamColorSwatches.light]
     // or both [StreamColorSwatches.dark].
     // Empirically, [lerp] is called even when the theme hasn't changed,
     // so this is an important optimization.
-    if (identical(this, other)) {
-      return this;
-    }
+    if (identical(a, b)) return a;
 
-    return _StreamColorSwatchesLerped(this, other, t);
+    return _StreamColorSwatchesLerped(a, b, t);
   }
 }
 
@@ -65,12 +63,12 @@ class _StreamColorSwatchesLerped extends StreamColorSwatches {
   _StreamColorSwatchesLerped(this.a, this.b, this.t);
 
   final StreamColorSwatches a;
-  final StreamColorSwatches? b;
+  final StreamColorSwatches b;
   final double t;
 
   @override
   StreamColorSwatch _computeForBaseColor(int base) =>
-    StreamColorSwatch.lerp(a.forBaseColor(base), b?.forBaseColor(base), t)!;
+    StreamColorSwatch.lerp(a.forBaseColor(base), b.forBaseColor(base), t)!;
 }
 
 
diff --git a/lib/widgets/theme.dart b/lib/widgets/theme.dart
index 39f2d77021..8a108d4be1 100644
--- a/lib/widgets/theme.dart
+++ b/lib/widgets/theme.dart
@@ -131,17 +131,17 @@ class DesignVariables extends ThemeExtension<DesignVariables> {
   }
 
   @override
-  DesignVariables lerp(DesignVariables? other, double t) {
+  DesignVariables lerp(DesignVariables other, double t) {
     if (identical(this, other)) {
       return this;
     }
     return DesignVariables._(
-      bgMain: Color.lerp(bgMain, other?.bgMain, t)!,
-      bgTopBar: Color.lerp(bgTopBar, other?.bgTopBar, t)!,
-      borderBar: Color.lerp(borderBar, other?.borderBar, t)!,
-      icon: Color.lerp(icon, other?.icon, t)!,
-      title: Color.lerp(title, other?.title, t)!,
-      streamColorSwatches: streamColorSwatches.lerp(other?.streamColorSwatches, t),
+      bgMain: Color.lerp(bgMain, other.bgMain, t)!,
+      bgTopBar: Color.lerp(bgTopBar, other.bgTopBar, t)!,
+      borderBar: Color.lerp(borderBar, other.borderBar, t)!,
+      icon: Color.lerp(icon, other.icon, t)!,
+      title: Color.lerp(title, other.title, t)!,
+      streamColorSwatches: StreamColorSwatches.lerp(streamColorSwatches, other.streamColorSwatches, t),
     );
   }
 }
diff --git a/test/widgets/stream_colors_test.dart b/test/widgets/stream_colors_test.dart
index b4ebbaa925..a3615c1919 100644
--- a/test/widgets/stream_colors_test.dart
+++ b/test/widgets/stream_colors_test.dart
@@ -40,17 +40,16 @@ void main() {
 
     group('lerp', () {
       test('on identical instances', () {
-        check(
-          StreamColorSwatches.light.lerp(StreamColorSwatches.light, 0.5)
-        ).identicalTo(StreamColorSwatches.light);
+        final light = StreamColorSwatches.light;
+        check(StreamColorSwatches.lerp(light, light, 0.5)).identicalTo(light);
 
-        check(
-          StreamColorSwatches.dark.lerp(StreamColorSwatches.dark, 0.5)
-        ).identicalTo(StreamColorSwatches.dark);
+        final dark = StreamColorSwatches.dark;
+        check(StreamColorSwatches.lerp(dark, dark, 0.5)).identicalTo(dark);
       });
 
       test('from light to dark', () {
-        final instance = StreamColorSwatches.light.lerp(StreamColorSwatches.dark, 0.4);
+        final instance = StreamColorSwatches
+          .lerp(StreamColorSwatches.light, StreamColorSwatches.dark, 0.4);
 
         const base1 = 0xff76ce90;
         final swatch1 = instance.forBaseColor(base1);