diff --git a/core/generator.ts b/core/generator.ts
index c7c26f15f..f948924d9 100644
--- a/core/generator.ts
+++ b/core/generator.ts
@@ -313,6 +313,9 @@ export class CodeGenerator {
       throw TypeError('Expecting valid order from block: ' + block.type);
     }
     const targetBlock = block.getInputTargetBlock(name);
+    if (!targetBlock && !block.getInput(name)) {
+      throw ReferenceError(`Input "${name}" doesn't exist on "${block.type}"`);
+    }
     if (!targetBlock) {
       return '';
     }
@@ -391,6 +394,9 @@ export class CodeGenerator {
    */
   statementToCode(block: Block, name: string): string {
     const targetBlock = block.getInputTargetBlock(name);
+    if (!targetBlock && !block.getInput(name)) {
+      throw ReferenceError(`Input "${name}" doesn't exist on "${block.type}"`);
+    }
     let code = this.blockToCode(targetBlock);
     // Value blocks must return code and order of operations info.
     // Statement blocks must only return code.
diff --git a/generators/dart/procedures.ts b/generators/dart/procedures.ts
index 5102432ad..0ecf6d210 100644
--- a/generators/dart/procedures.ts
+++ b/generators/dart/procedures.ts
@@ -35,8 +35,17 @@ export function procedures_defreturn(block: Block, generator: DartGenerator) {
       generator.INDENT,
     );
   }
-  const branch = generator.statementToCode(block, 'STACK');
-  let returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  let branch = '';
+  if (block.getInput('STACK')) {
+    // The 'procedures_defreturn' block might not have a STACK input.
+    branch = generator.statementToCode(block, 'STACK');
+  }
+  let returnValue = '';
+  if (block.getInput('RETURN')) {
+    // The 'procedures_defnoreturn' block (which shares this code)
+    // does not have a RETURN input.
+    returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  }
   let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.
diff --git a/generators/dart/text.ts b/generators/dart/text.ts
index 501619e03..6bb2bea82 100644
--- a/generators/dart/text.ts
+++ b/generators/dart/text.ts
@@ -128,10 +128,12 @@ export function text_charAt(
       return [code, Order.UNARY_POSTFIX];
     }
     case 'LAST':
-      at = 1;
-    // Fall through.
     case 'FROM_END': {
-      at = generator.getAdjusted(block, 'AT', 1);
+      if (where === 'LAST') {
+        at = 1;
+      } else {
+        at = generator.getAdjusted(block, 'AT', 1);
+      }
       const functionName = generator.provideFunction_(
         'text_get_from_end',
         `
@@ -140,7 +142,7 @@ String ${generator.FUNCTION_NAME_PLACEHOLDER_}(String text, num x) {
 }
 `,
       );
-      const code = functionName + '(' + text + ', ' + at + ')';
+      const code = `${functionName}(${text}, ${at})`;
       return [code, Order.UNARY_POSTFIX];
     }
     case 'RANDOM': {
diff --git a/generators/javascript/procedures.ts b/generators/javascript/procedures.ts
index a835271e7..e0a055217 100644
--- a/generators/javascript/procedures.ts
+++ b/generators/javascript/procedures.ts
@@ -38,8 +38,17 @@ export function procedures_defreturn(
       generator.INDENT,
     );
   }
-  const branch = generator.statementToCode(block, 'STACK');
-  let returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  let branch = '';
+  if (block.getInput('STACK')) {
+    // The 'procedures_defreturn' block might not have a STACK input.
+    branch = generator.statementToCode(block, 'STACK');
+  }
+  let returnValue = '';
+  if (block.getInput('RETURN')) {
+    // The 'procedures_defnoreturn' block (which shares this code)
+    // does not have a RETURN input.
+    returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  }
   let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.
diff --git a/generators/lua/procedures.ts b/generators/lua/procedures.ts
index 07003aee9..79dc58aa2 100644
--- a/generators/lua/procedures.ts
+++ b/generators/lua/procedures.ts
@@ -38,8 +38,17 @@ export function procedures_defreturn(
       generator.INDENT,
     );
   }
-  let branch = generator.statementToCode(block, 'STACK');
-  let returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  let branch = '';
+  if (block.getInput('STACK')) {
+    // The 'procedures_defreturn' block might not have a STACK input.
+    branch = generator.statementToCode(block, 'STACK');
+  }
+  let returnValue = '';
+  if (block.getInput('RETURN')) {
+    // The 'procedures_defnoreturn' block (which shares this code)
+    // does not have a RETURN input.
+    returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  }
   let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.
diff --git a/generators/lua/text.ts b/generators/lua/text.ts
index defbbaf99..350b86313 100644
--- a/generators/lua/text.ts
+++ b/generators/lua/text.ts
@@ -132,8 +132,6 @@ export function text_charAt(
   // Get letter at index.
   // Note: Until January 2013 this block did not have the WHERE input.
   const where = block.getFieldValue('WHERE') || 'FROM_START';
-  const atOrder = where === 'FROM_END' ? Order.UNARY : Order.NONE;
-  const at = generator.valueToCode(block, 'AT', atOrder) || '1';
   const text = generator.valueToCode(block, 'VALUE', Order.NONE) || "''";
   let code;
   if (where === 'RANDOM') {
@@ -154,6 +152,8 @@ end
     } else if (where === 'LAST') {
       start = '-1';
     } else {
+      const atOrder = where === 'FROM_END' ? Order.UNARY : Order.NONE;
+      const at = generator.valueToCode(block, 'AT', atOrder) || '1';
       if (where === 'FROM_START') {
         start = at;
       } else if (where === 'FROM_END') {
diff --git a/generators/php/procedures.ts b/generators/php/procedures.ts
index bd114cd0d..acf84aea6 100644
--- a/generators/php/procedures.ts
+++ b/generators/php/procedures.ts
@@ -60,8 +60,17 @@ export function procedures_defreturn(block: Block, generator: PhpGenerator) {
       generator.INDENT,
     );
   }
-  const branch = generator.statementToCode(block, 'STACK');
-  let returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  let branch = '';
+  if (block.getInput('STACK')) {
+    // The 'procedures_defreturn' block might not have a STACK input.
+    branch = generator.statementToCode(block, 'STACK');
+  }
+  let returnValue = '';
+  if (block.getInput('RETURN')) {
+    // The 'procedures_defnoreturn' block (which shares this code)
+    // does not have a RETURN input.
+    returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  }
   let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.
diff --git a/generators/python/procedures.ts b/generators/python/procedures.ts
index 798d6d55a..51d2ee9a3 100644
--- a/generators/python/procedures.ts
+++ b/generators/python/procedures.ts
@@ -60,8 +60,17 @@ export function procedures_defreturn(block: Block, generator: PythonGenerator) {
       generator.INDENT,
     );
   }
-  let branch = generator.statementToCode(block, 'STACK');
-  let returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  let branch = '';
+  if (block.getInput('STACK')) {
+    // The 'procedures_defreturn' block might not have a STACK input.
+    branch = generator.statementToCode(block, 'STACK');
+  }
+  let returnValue = '';
+  if (block.getInput('RETURN')) {
+    // The 'procedures_defnoreturn' block (which shares this code)
+    // does not have a RETURN input.
+    returnValue = generator.valueToCode(block, 'RETURN', Order.NONE) || '';
+  }
   let xfix2 = '';
   if (branch && returnValue) {
     // After executing the function body, revisit this block for the return.